EVIDENCE AND REASONING
27. Evidence and Reasoning. We have seen in the last chapter that
the chief value of making a brief is that in the first place it lays out
your reasoning so that you can scrutinize it in detail; and that in the
second place it displays the foundations of your reasoning on facts
which cannot be contested. In this chapter we shall consider what
grounds give validity to evidence and to reasoning.
Where the facts which you bring forward come from persons with
first-hand knowledge of them, they are direct evidence; where you must
establish them by reasoning from other facts they are indirect evidence,
and in the latter case reasoning is an essential part of establishing
the facts. In this chapter, therefore, I shall speak first of direct
evidence, then of indirect, and then pass on to consider a few of the
simpler principles which govern reasoning.
In ordinary usage the word "evidence" is pretty vague, and means
anything that will help to establish one side or another of any
question, whether of fact or of policy. The word, however, comes
ultimately from the law, where it is used for the testimony, either oral
or written or material, which is brought in to establish the truth of
assertions about fact: evidence is set before the jury, which under the
common law decides questions of fact. In almost any argument of policy,
however, we use facts as reasons for or against the policy which is in
question, and therefore inmost cases we must use evidence to establish
these facts; in many cases, when the facts are established there is no
further disagreement about the policy. For example, in arguments for and
against state prohibition of the liquor trade, it is an essential fact
to determine whether in status where prohibition has been tried it has
failed or succeeded, and another essential fact whether under similar
conditions a combination of high license and local option has or has not
produced less drunkenness. Both are extremely complicated and difficult
facts to decide; but if clear evidence can be brought forward to
establish them, reasonable-minded people would generally hold as settled
the question of the policy which should be adopted. Similarly, an
argument for the popular election of senators would undoubtedly make
large use of the alleged fact that, in elections by the legislatures,
there has been much undue interference by special interests and rich
corporations; and the assertion of this fact would have to be supported
by evidence. If this fact were thus clearly established, it would be
recognized as a strong reason for a change in our present policy. In the
interest of clearness of thought it is worth while to remember this
distinction; for, as we shall see, it is only by so doing that we can
determine when the ordinary rules of logic do and when they do not apply
to the processes of reasoning on which argument is based. I shall speak
here, therefore, of the evidence for facts, and of the reasons for or
against a policy.
It may be said in passing that the highly complicated rules of evidence
at the common law have practically nothing to do with our present
subject, for they spring from very special conditions, and have been
molded by very special purposes. Their object is to establish, so far as
is possible, principles which will apply to all cases of a like nature;
and they therefore rule out many facts and much evidence which outside
the court we all use without hesitation in making up our minds. The jury
system has had a curious and interesting history: and judges have built
up hedges around juries which seem to the layman merely technical, and
unnecessary for the ends of justice.[14] Yet though the sweeping away of
many of these rules from time to time shows that there has been and
perhaps still is justice in this view, one must remember that the whole
common law is based on the application of principles already established
by earlier cases to new cases of like character; and that great care
must therefore be used not to establish principles which may interfere
with the even distribution of justice in the long run (see on this point
S.R. Gardiner, p. 103). Even if in single cases the rule of evidence
that forbids hearsay evidence works an injustice, yet in the long run it
is obvious both that, if hearsay were allowed, litigants would take less
trouble to get original evidence, and that much hearsay is thoroughly
untrustworthy.
Another reason why the rules of evidence at the common law have little
bearing on the arguments of everyday life is like that which makes it
unwise to dwell much on the burden of proof: there is no one either
competent or interested to enforce the exclusion. Assertion and rumor
must be more than palpably vague before the ordinary man will of his own
initiative take the trouble to scrutinize it; and even in refuting such
material you must make its untrustworthiness very patent if you expect
to make ordinary readers distrust it seriously.
28. Direct and Indirect Evidence. When we come now to consider how we
establish facts, whether single or complex, we find that, both to aid
our own judgment and to convince other people, we rely on evidence. We
have seen that evidence falls roughly into two classes: either it comes
from persons who testify out of their own observation and experience, or
it comes indirectly through reasoning from facts and principles already
established or granted. The two kinds of evidence run into each other,
and the terms commonly used to describe them vary: "direct evidence" is
not infrequently, as in Huxley's argument (see p. 240), called
"testimonial," and "indirect evidence," as in the same argument and in
the opinion of Chief Justice Shaw, quoted below, is called
"circumstantial." On the whole, however, the opposition between the two
classes, so far as it is of practical importance, may best be indicated
by the terms "direct evidence" and "indirect evidence." The distinction
between the two classes is made clear in the following extract from the
opinion of Chief Justice Shaw of the Massachusetts Supreme Court. It
will be noticed that it is the same doctrine as that laid down by Huxley
(see p. 240).
The distinction, then, between direct and circumstantial evidence is
this. Direct or positive evidence is when a witness can be called to
testify to the precise; fact which is the subject of the issue in trial;
that is, in a case of homicide, that the party accused did cause the
death of the deceased. Whatever may be the kind or force of the
evidence, this is the fact to be proved. But suppose no person was
present on the occasion of the death,--and of course no one can be
called to testify to it,--is it wholly unsusceptible of legal proof?
Experience has shown that circumstantial evidence may be offered in such
a case; that is, that a body of facts may be proved of so conclusive a
character, as to warrant a firm belief of the fact, quite as strong and
certain as that on which discreet men are accustomed to act in relation
to their most important concerns....
Each of these modes of proof has its advantages and disadvantages; it is
not easy to compare their relative value. The advantage of positive
evidence is, that you have the direct testimony of a witness to the fact
to be proved, who, if he speaks the truth, saw it done; and the only
question is, whether he is entitled to belief. The disadvantage is, that
the witness may be false and corrupt, and the case may not afford the
means of detecting his falsehood.
But in a case of circumstantial evidence where no witness can testify
directly to the fact to be proved, you arrive at it by a series of other
facts, which by experience we have found so associated with the fact in
question, as in the relation of cause and effect, that they lead to a
satisfactory and certain conclusion; as when footprints are discovered
after a recent snow, it is certain that some animated being has passed
over the snow since it fell; and, from the form and number of the
footprints, it can be determined with equal certainty, whether it was a
man, a bird, or a quadruped. Circumstantial evidence, therefore, is
founded on experience and observed facts and coincidences, establishing
a connection between the known and proved facts and the fact sought to
be proved.[15]
Under the head of direct evidence, as I shall use the term, would fall
the evidence of material objects: in an accident case, for example, the
scar of a wound may be shown to the jury; or where the making of a park
is urged on a city government, the city council may be taken out to see
the land which it is proposed to take. Though such evidence is not
testimony, it is direct evidence, for it is not based on reasoning and
inference.
29. Direct Evidence. Direct evidence is the testimony of persons
who know about the fact from their own observation: such is the
testimony of the witnesses to a will that they saw the testator sign it,
the testimony of an explorer that there are tribes of pygmies in Africa,
the testimony of a chemist to the constituents of a given alloy, or of a
doctor to the success of a new treatment. Every day of our lives we are
giving and receiving direct evidence; and of this evidence there is
great variety in value.
In the first place, no one should place too much reliance on his own
casual observations. It is notorious that we see what we expect to see;
and no one who has not deliberately set himself to observe the fact can
realize how much of what he thinks is observation is really inference
from a small part of the facts before him. I feel a slight tremor run
through the house with a little rattling of the windows, and assume that
a train has gone by on the railroad below the hill a hundred yards away:
as a matter of fact it may have been one of the slight earthquake shocks
which come every few years in most parts of the world. The mistakes that
most of its make in recognizing people are of the same sort: from some
single feature we reason to an identity that does not exist.
Of recent years psychologists have set themselves to getting some
accurate facts as to this inaccuracy of human observation, and various
experiments have been tried. Here is an account of one:
There was, for instance, two years ago in Göttingen a meeting of a
scientific association, made up of jurists, psychologists, and
physicians, all, therefore, men trained in careful observation.
Somewhere in the same street there was that evening a public festivity
of the carnival. Suddenly, in the midst of the scholarly meeting, the
doors open, a clown in highly colored costume rushes in in mad
excitement, and a negro with a revolver in hand follows him. In the
middle of the hall first the one, then the other, shouts wild phrases;
then the one falls to the ground, the other jumps on him; then a shot,
and suddenly both are out of the room. The whole affair took less than
twenty seconds. All were completely taken by surprise, and no one, with
the exception of the president, had the slightest idea that every word
and action had been rehearsed beforehand, or that, photographs had been
taken of the scene. It seemed most natural that the president should beg
the members to write down individually an exact report, inasmuch as he
felt sure that the matter would come before the courts. Of the forty
reports handed in, there was only one whose omissions were calculated as
amounting to less than twenty per cent of the characteristic acts;
fourteen had twenty to forty per cent of the facts omitted; twelve
omitted forty to fifty per cent, and thirteen still more than fifty per
cent. But besides the omissions there were only six among the forty
which did not contain positively wrong statements; in twenty-four
papers up to ten per cent of the statements were free inventions, and in
ten answers--that is, in one fourth of the papers--more than ten per
cent of the statements were absolutely false, in spite of the fact that
they all came from scientifically trained observers. Only four persons,
for instance, among forty noticed that the negro had nothing on his
head; the others gave him a derby, or a high hat, and so on. In addition
to this, a red suit, a brown one, a striped one, a coffee-colored
jacket, shirt sleeves, and similar costume were invented for him. He
wore in reality white trousers and a black jacket with a large red
neck-tie. The scientific commission which reported the details of the
inquiry came to the general statement that the majority of the observers
omitted or falsified about half of the processes which occurred
completely in their field of vision. As was to be expected, the judgment
as to the time duration of the act varied between a few seconds and
several minutes.[16]
Another type of cases in which our direct testimony would be valueless
is legerdemain: we think that we actually see rabbits taken out of our
neighbor's hat, or his watch pounded in a mortar and presently shaken
whole and sound out of an empty silk handkerchief; and it is only by
reasoning that we know our eyes have been deceived.
It is obvious, therefore, that to question a man's evidence is not
always to call him a liar; in most cases it is rather to question the
accuracy of his inferences from such part of the facts as he actually
grasped. In science no important observation is accepted until the
experiments have been repeated and checked by other observers. Indeed,
most of the progress of science is due to the repetition of experiments
by observers who notice some critical phenomena which their predecessors
have missed.
With this qualification, that human observation is always fallible,
good direct evidence is on the whole the most convincing evidence that
you can use. If you can establish a fact by the mouths of trustworthy
witnesses, making your readers recognize that these witnesses had good
opportunities of observation and a competent knowledge of the subject,
you will generally establish your point. In case of an accident in a
street car it is the custom of many companies to require their
conductors to take down immediately the names of a few of the most
respectable-looking of the passengers, who may be called as witnesses in
case of a lawsuit. All the observations of science, and most of the
facts brought before juries in courts of law, as well as the multitude
of lesser and greater facts which we accept in everyday life, get their
authority from this principle.
In the arguments of school and college you may not make much use of
direct evidence, for they do not often turn on single, simple facts.
Even here, however, cases arise where you must call in the direct
testimony of witnesses. If you were arguing that secret societies should
be abolished in a certain school, and wished to show that such societies
had led to late hours, playing cards for money, and drinking, you would
need direct evidence. If you were arguing that the street railroad
company of your city should be obliged to double track a certain part of
its line, you would need direct evidence of the delays and crowding of
cars with a single track.
When you are using direct evidence you should make it clear that the
person from whom it comes is a competent witness, that he has been in a
position to know the facts at first hand, and that, if necessary, he has
had the proper training to understand their meaning. In the case of an
automobile accident a man who had never run a car would not be the best
sort of witness as to the actions of the chauffeur, nor a man who had
never sailed a boat as to what happened in a collision between two
sailboats. In a scientific matter the observations of a beginner would
not carry weight as against those of a man who had used a microscope for
many years.
The witness, too, must be shown to be free from bias, whether practical
or theoretical. It is a well-known fact that men differ greatly in the
clearness of their eyesight in observing the stars, and that men who are
gifted with exceptional eyesight may make valuable discoveries with
inferior instruments; but if such a man has espoused a theory, say, as
to the nature of the rings of Saturn, and is known to defend it
passionately, his evidence concerning what he had seen is bound to be
somewhat discounted.
Even official reports cannot be trusted without scrutiny.
The fact is that many things conspire to make an official report
constrained and formal. There is the natural desire of every man to put
the best face on things for himself as he sets his case before the
government and the world; subordinates must be let off leniently; you
must live with them, and it impairs comfort to have them sullen. To make
a statement unpleasant to a superior might be construed as
insubordination. The public welfare makes it imperative to tell a
flattering tale. The temptation is constant to tell not quite the whole
truth, and nothing but the truth. There are important suppressions of
fact in the official records, none more so, perhaps, than as regards
Chancellorsville.[17]
If you happen to be dealing with a historical matter, where the
testimony comes from a more or less remote past, and the evidence is
scrappy and defective, you must be still more careful.
The great English historian, the late S.R. Gardiner, in his
examination of the evidence on the Gunpowder Plot of 1605, wrote as
follows about the difficulties of dealing with historical evidence:
It seems strange to find a writer so regardless of what is, in these
days, considered the first canon of historical inquiry, that evidence
worth having must be almost entirely the evidence of contemporaries who
are in a position to know something about that which they assert. It is
true that this canon must not be received pedantically. Tradition is
worth something, at all events when it is not too far removed from its
source. If a man whose character for truthfulness stands high, tells me
that his father, also believed to be truthful, seriously informed him
that he had seen a certain thing happen, I should be much more likely to
believe that it was so than if a person, whom I knew to be untruthful,
informed me that he had himself witnessed something at the present day.
The historian is not bound, as the lawyer is, to reject hearsay
evidence, because it is his business to ascertain the truth of
individual assertions, whilst the lawyer has to think of the bearing of
the evidence not merely on the case of the prisoner in the dock, but on
an unrestricted number of possible prisoners, many of whom would be
unjustly condemned if hearsay evidence were admitted. The historian is,
however, bound to remember that evidence grows weaker with each link of
the chain. The injunction, "Always leave a story better than you found
it," is in accordance with the facts of human nature. Each reporter
inevitably accentuates the side of the narrative which strikes his
fancy, and drops some other part which interests him less. The rule laid
down by the late Mr. Spedding, "When a thing is asserted as a fact,
always ask who first reported it, and what means he had of knowing the
truth," is an admirable corrective of loose traditional stories.
A further test has to be applied by each investigator for himself. When
we have ascertained, as far as possible, on what evidence our knowledge
of an alleged fact rests, we have to consider the inherent probability
of the allegation. Is the statement about it in accordance with the
general workings of human nature, or with the particular working of the
nature of the persons to whom the action in question is ascribed? Father
Gerard,[18] for instance, lavishly employs this test. Again and again he
tells us that such and such a statement is incredible, because, amongst
other reasons, the people about whom it was made could not possibly have
acted in the way ascribed to them. If I say in any of these cases that
it appears to me probable that they did so act, it is merely one
individual opinion against another. There is no mathematical certainty
on either side. All we can respectively do is to set forth the reasons
which incline us to one opinion or another, and leave the matter to
others to judge as they see fit.
It will be necessary hereafter to deal at length with father Gerard's
attack upon the evidence, hitherto accepted as conclusive, of the facts
of the plot. A short space may be allotted to the reasons for rejecting
his preliminary argument, that it was the opinion of some
contemporaries, and of some who lived in a later generation, that
Salisbury contrived the plot in part, if not altogether. Does he realize
how difficult it is to prove such a thing by any external evidence
whatever? If hearsay evidence can be taken as an argument of
probability, and in some cases of strong probability, it is where some
one material fact is concerned. For instance, I am of opinion that it is
very likely that the story of Cromwell's visit to the body of Charles I
on the night after the king's execution is true, though the evidence is
only that Spence heard it from Pope, and Pope heard it, mediately or
immediately, from Southampton, who, it is alleged, saw the scene with
his own eyes. It is very different when we are concerned with evidence
as to an intention necessarily kept secret, and only exhibited by overt
acts in such form as tampering with documents, suggesting false
explanation of evidence, and so forth. A rumor that Salisbury got up the
plot is absolutely worthless; a rumor that he forged a particular
instrument would be worth examining, because it might have proceeded
from some one who had seen him do it.[19]
While it is rare to find a man of whom it may justly be said that there
is no partition between his memory and his imagination, yet there are
few of us who can be sure of facts in past matters which touch our
feelings. We cannot help to some degree reconstructing events as they
fade away into the past: we forget those parts of an event which did not
at the time sharply touch our imagination, and those which did move us
take on an overshadowing importance. Therefore the further away the
events which the evidence is to reconstruct, the more care we must take
to scrutinize it to see if there are signs of bias.
To test the value of direct evidence, therefore, as to single and simple
facts, consider whether the evidence comes from a specifically named
source, whether there is any likelihood that the witness may have been
honestly deceived in his observation, whether he had a good opportunity
to know the facts and a sufficient knowledge of the subject about which
he is giving evidence, and, finally, whether he was reasonably free from
bias in the matter.
Whenever you use direct evidence, however, it must be direct. To assert
that "every one knows that secret societies in a certain school have led
to immoral practices," is not direct evidence, nor to declare that "the
best authorities in the city are agreed that the company should lay
double tracks on a certain street." Such assertions are apt to be the
most roundabout sort of hearsay. Try cross-examining the next man you
hear make this kind of sweeping assertion, in order to see what he
really knows of the facts, and you will soon find how recklessly such
assertions are made. You constantly hear grave statements of facts whose
ultimate basis is the imagination of some enterprising newspaper
reporter; yet careful and truthful people pass them on as if they were
indubitable.
The news columns of the papers are largely written by young fellows just
out of high school, who will declare the whole gospel on subjects with
which they have a half hour's acquaintance, yet most people never
question their statements. The printed page, whether of a hook, a
magazine, or a newspaper, casts a spell on our judgment. Such floating
assertions, with no one to father them, are of no value whatever. If you
have to use statements in a newspaper as direct evidence, either take
them from a newspaper which is recognized as careful about facts, or
else look up the matter in two or three papers, and show that their
testimony agrees.
On the other hand, a specific name, with a specific reference to volume
and page, will go a long way to give your readers confidence in the
evidence you adduce. And rightly so, for one man with a name and address
is worth hundreds of unnamed "highest authorities"; and the more
specifically you refer to him and to his evidence, the more likely you
will be to win over your audience to your view.
A famous and effective example of the use of specific names to give
authority to an argument, and the incidental refutation of a vague and
loose assertion, is found in Lincoln's address at Cooper Institute, in
the first part of which he took up Senator Douglas's statement that "our
fathers, when they framed the government under which we live, understood
this question just as well as, and even better than, we do now," with
the implication that they intended to forbid the federal government to
control slavery in the federal territories. Lincoln showed that "our
fathers who framed the government under which we live" must be the
makers of the Constitution: and then he proceeded to show just what
action each one of them, so far as record had been preserved, had taken
on the question. Here is a passage from his argument:
The question of Federal control in the Territories seems not to have
been directly before the convention which framed the original
Constitution; and hence it is not recorded that the "thirty-nine," or
any of them, while engaged on that instrument, expressed any opinion on
that precise question.
In 1789, by the first Congress which sat under the Constitution, an act
was passed to enforce the ordinance of 1787, including the prohibition
of slavery in the Northwestern Territory. The bill for this act was
reported by one of the "thirty-nine"--Thomas Fitzsimmons, then a member
of the House of Representatives from Pennsylvania. It went through all
its stages without a word of opposition, and finally passed both
branches without ayes and nays, which is equivalent to a unanimous
passage. In this Congress there were sixteen of the thirty-nine fathers
who framed the original Constitution. They were John Langdon, Nicholas
Gilman, William S. Johnson, Roger Sherman, Robert Morris, Thomas
Fitzsimmons, William Few, Abraham Baldwin, Rufus King, William Paterson,
George Clymer, Richard Bassett, George Read, Pierce Butler, Daniel
Carroll, and James Madison.
This shows that, in their understanding, no line dividing local from
Federal authority, nor anything in the Constitution, properly forbade
Congress to prohibit slavery in the Federal territory; else both their
fidelity to correct principle, and their oath to support the
Constitution, would have constrained them to oppose the prohibition.
Again, George Washington, another of the "thirty-nine," was then
President of the United States and as such approved and signed the bill,
thus completing its validity as a law, and thus showing that, in his
understanding, no line dividing local from Federal authority, nor
anything in the Constitution, forbade the Federal Government to control
as to slavery in Federal territory.
No great while after the adoption of the original Constitution, North
Carolina ceded to the Federal Government the country now constituting
the State-of Tennessee; and a few years later Georgia ceded that which
now constitutes the States of Mississippi and Alabama. In both deeds of
cession it was made a condition by the ceding States that the Federal
Government should not prohibit slavery in the ceded country. Besides
this, slavery was then actually in the ceded country. Under these
circumstances, Congress, on taking charge of these countries, did not
absolutely prohibit slavery in them. But they did interfere with
it--take control of it----even there, to a certain extent. In 1798
Congress organized the Territory of Mississippi. In the act of
organization they prohibited the bringing of slaves into the Territory
from any place without the United States, by fine, and giving freedom to
slaves so brought. This act passed both branches of Congress without
yeas and nays. In that Congress were three of the "thirty-nine" who
framed the original Constitution. They were John Langdon, George Read,
and Abraham Baldwin. They all probably voted for it. Certainly they
would have placed their opposition to it upon record if, in their
understanding, any line dividing local from Federal authority, or
anything in the Constitution, properly forbade the Federal Government to
control as to slavery in Federal territory.
In the end this exact statement of names, for which he had prepared
himself with such laborious care, enabled Lincoln to sum up with
absolute conclusiveness:
The cases I have mentioned are the only acts of the "thirty-nine," or of
any of them, upon the direct issue, which I have been able to discover.
To enumerate the persons who thus acted as being four in 1784, two in
1787, seventeen in 1789, three in 1798, two in 7804, and two in
1819-1820, there would be thirty of them. But this would be counting
John Langdon, Roger Sherman, William Few, Rufus King, and George Read
each twice, and Abraham Baldwin three times. The true number of those of
the "thirty-nine" whom I have shown to have acted upon the question
which, by the text, they understood better than we, is twenty-three,
leaving sixteen not shown to have acted upon it in any way.
Here, then, we have twenty-three out of our thirty-nine fathers "who
framed the government under which we live," who have, upon their
official responsibility and their corporal oaths, acted upon the very
question which the text affirms they "understood just as well, and even
better, than we do now"; and twenty-one of them--a clear majority of the
whole "thirty-nine"--so acting upon it as to make them guilty of gross
political impropriety and willful perjury if, in their understanding,
any proper division between local and Federal authority, or anything in
the Constitution they had made themselves, and sworn to support, forbade
the Federal Government to control as to slavery in the Federal
territories. Thus the twenty-one acted; and, as actions speak louder
than words, so actions under such responsibility speak still louder.
When you come to evidence about a large and complex state of affairs,
which is the kind of fact that so many of the arguments of practical
life deal with, though you will still be dealing with a fact, yet the
very nature of the fact changes the value and the character of your
evidence. It is a comparatively simple matter to determine whether a
certain woman faced forward or backward as she was getting off a street
car, or whether the eggs of a sea urchin do or do not begin to germinate
under the influence of a certain chemical substance; but it is far from
simple to determine whether a free elective course has or has not inured
to greater intelligence and cultivation in the graduates of a certain
college, or whether the graduates of another college where the classical
course is maintained have keener and more flexible minds and more
refined tastes as a result of their study of the classics. In such cases
as these the citing of direct evidence brings on you difficulties of a
different kind from those you face when you are establishing a single,
simple fact. Here you will usually depend on two main sources of
evidence: statistics, and the evidence of recognized authorities on the
subject.
30. Statistics. Statistics, which are collections of figures, are
notoriously treacherous. On many important subjects, such, for example,
as the practical effect of the elective system, it is impossible to get
them; and on many other subjects, such as the effects of a protective
tariff, they must be had in so enormous masses, if they are to be
trusted at all, that only profound students can handle them. Where the
facts are complicated, and interests are tangled, moreover, many sets of
figures may enter into the question, as notably in the case of a tariff;
so clearly is this difficulty now recognized that Congress has
authorized a tariff board made up of distinguished students of economics
and men of long experience in dealing with tariff matters to collect and
study the facts and make recommendations based on them. Similarly, with
the investigation into the liquor question made fifteen years ago by the
Committee of Fifty: the whole question had been so tangled by assertion
and counter-assertion that it became desirable to have an investigation
into the facts by men of recognized ability and impartiality.[20]
In general, to use statistics safely you need a wide acquaintance with a
subject, especially where the question is in any way mixed up with men's
feelings, whether through politics or not. All the statistics we have
make dead against great armaments and preparation for war; yet while
human nature is what it is, necessary prudence seems to require every
nation of any size to have them. A very little human nature will upset a
very great body of statistics. Furthermore, in most human affairs
results are produced by a multiplicity of causes; and though statistics
may throw light on three quarters of all the causes that are potent in
any given case, yet the other quarter which are irreducible to definite
statement may wholly alter the result. If you are using statistics in
your argument, therefore, as evidence of some large and complex fact,
you should usually justify them to some extent by showing that there are
no counteracting forces which they do not cover.
With this precaution, however, statistics are the foundation of most
arguments on large questions. If you were arguing in favor of the
purchase of local waterworks, you would present figures showing the
number of houses using the public water supply, the rates paid, the
profits of the company, the exact points at which public control could
work economies. If you were arguing for a rule that no man shall play on
a university team until he has been registered a year at the university,
you would need statistics to show how many men would be affected by the
rule. If you were arguing for a single session at a school instead of
two, you would show exactly how many students in the school live more
than a mile away from the building. In every case where statistics can
be presented in such a way as to make clear that they fairly cover the
ground, they are most valuable evidence. They give the argument the
effect of being founded on a rock. If it be obvious that the statistics
have been freshly gathered, and are not merely casual and second-hand
gleanings, they have still greater effect, for then they have a
secondary force in testifying to the personal knowledge that the witness
has of the subject. We shall see later the danger of the fallacy of
generalizing on too narrow a basis: a generalization based on a good
body of statistics runs no danger of this fallacy.
31. The Opinion of Recognized Authorities. The other chief source
of evidence to establish a fact which consists of a large and complex
state of affairs is the opinion of recognized authorities on the
subject. The strength of such evidence depends on whether the audience
will accept the person you cite as having authority on the matter. Most
of us read some newspaper or periodical in the opinions of which we have
confidence, because they seem to be based on investigation and competent
knowledge. The annual report of the Secretary of the Treasury is
excellent evidence on the state of the national finances. The reports of
presidents of colleges are excellent evidence from authorities on such
questions as the value of the elective system or the effect of raising
the standard of admission. The report of a dean or of a schoolmaster on
the value of organized athletics is effective if the audience knows that
he likes out-of-door sports and takes time to see the games. Evidence
drawn from an authority who is likely to be used by the other side is
doubly effective, since your readers recognize that his competence is
admitted.
If a man has given his life to the study of a subject and has published
books that are of recognized authority, his evidence will be of especial
weight. Mr. Bryce's opinion on all questions concerning a state of
affairs in this country would be recognized at once as weighty, for he
has given time and study to collecting the multitude of small facts
which constitute the large fact. His opinion that political honesty is
increasing with us has brought comfort to many good citizens who had
grown despondent over the accounts of recurrent rascality in the
newspapers and magazines. This is a typical case for the citation of
authorities; for the facts are enormous in number, very widely
scattered, and often contradictory. Only a man who has taken the pains
to keep himself constantly informed, whose judgment has been trained by
long consideration and comparison of the facts, and who is born with the
judicial temperament can attain the authority of Mr. Bryce.
There will be cases on which you will have the right to put yourself
forward as an authority, for on many subjects which fall within the
range of undergraduates their knowledge is first-hand. On all questions
of athletics, especially, an undergraduate is apt to have freshly in
mind a considerable mass of facts. In the same way, on the results of
certain requirements for admission to college, you can speak from recent
experience. In matters concerning your own city, too, you may have
original knowledge.
If you are going to put yourself forward as an authority, however, you
must round out your knowledge of the facts by extending it beyond your
own personal experience. If it is a question of entrance requirements,
you cannot stop with your own experience, or even with that of your own
class at school. You must go back to the records of a number of classes
before and perhaps after your own, and talk them over with the principal
of the school, to see whether there are any special circumstances which
affect any of them. If you are arguing for or against a change in the
present rules of football, you would have to go beyond the games of your
own college team, and beyond those of the present season. If, for
example, it were a question of amending the rules concerning the forward
pass, you could not speak with full authority unless you had looked up
the accounts of the principal games for two or three years at any rate.
If you put yourself forward, then, as a witness on one of these cases of
complicated facts, you must make it clear to your readers that you have
a right to be considered such. If you have the right, it would be folly
to hide your light under a bushel.
An example of the care which is taken by men who have made themselves
authorities on their subjects is to be found in the following passage
from President Eliot's address, "A Wider Range of Electives in College
Admission Requirements."[21] Notice how broad a basis he lays for his
conclusions both in facts and in the opinions of other authorities.
What should be the grounds of a just valuation of all the subjects
that can be presented at admission examinations which include
numerous options?
That question introduces us to a difficult inquiry. It is, of course,
not an intelligent method to attribute a value to each subject in
accordance with the time devoted to the examination in that subject.
What clue have we toward a better mode of determining the value
which ought to be attributed to each of the numerous electives,
when the young men cannot present all the permitted subjects,
and hardly three fifths of them, indeed, if the range is adequately
widened? I believe that the best criterion for determining the value
of each subject is the time devoted to that subject in schools which
have an intelligent program of studies. The Committee of Ten[22]
examined the number of subjects used in about two hundred of the
best secondary schools in this country, and the time-allotments for
the several subjects. They found a great variety of practice as to
both selection of subjects and time-allotments. You can hardly say
that there is an accepted time-allotment in these secondary schools
for any subject--not even for the old traditional subjects. The
time-allotments differ widely in different parts of the country, and
even in different schools in the same part of the country. If, then,
we are to determine by school time-allotments the valuations of the
different subjects, prescribed and elective, which may enter into
admission examinations, we must have some sort of standard programs for
secondary schools. At present (1896) I know no programs which can answer
that purpose, except the provisional programs of the Committee of Ten.
They may fairly be said to be the best-studied programs now before the
country, and to represent the largest amount of professional consent,
simply because they are the result of the work, first, of ninety school
and college teachers, divided into nine different conferences by
subject, and secondly, of ten representative teachers combining and
revising the work of the conferences, with careful reference to the
present condition of American schools.
32. Indirect Evidence. The term "indirect evidence" may be used for
all evidence as to fact in which reasoning consciously plays a part.
Without it we should be helpless in large regions of our intellectual
life, notably in science and history, and constantly in everyday life.
Clearly the line between direct and indirect evidence is vague and
uncertain; it is one of the first things learned in psychology that our
perceptions and judgments of things about us are almost never based
exclusively on the testimony of our senses, and that we are all the time
jumping to conclusions from very partial observations.
Professor Münsterberg gives the following example from his own
experience of this unintentional substitution of indirect evidence for
direct:
Last summer I had to face a jury as witness in a trial. While I was with
my family at the seashore my city house had been burglarized and I was
called upon to give an account of my findings against the culprit whom
they caught with part of the booty. I reported under oath that the
burglars had entered through a cellar window, and then described what
rooms they had visited. To prove, in answer to a direct question, that
they had been there at night, I told that I had found drops of candle
wax on the second floor. To show that they intended, to return, I
reported that they had left a large mantel clock, packed in wrapping
paper, on the dining-room table. Finally, as to the amount of clothes
which they had taken, I asserted that the burglars did not get more than
a specified list which I had given the police.
Only a few days later I found that every one of these statements was
wrong. They had not entered through the window, but had broken the lock
of the cellar door; the clock was not packed by them in wrapping paper,
but in a tablecloth; the candle droppings were not on the second floor,
but in the attic; the list of lost garments was to be increased by seven
more pieces; and while my story under oath spoke always of two burglars,
I do not know that there was more than one.[23]
Constantly in everyday life we make offhand assertions in the full
belief that we are giving direct evidence, when as a matter of fact we
are announcing inferences. The distinction is of importance in many
ways, and not least as a means of avoiding heat in argument; for to
question a man's inference is much less likely to make him angry than to
deny his statement of fact.
For the practical purposes of argument we may let the distinction
between observation and inference, and consequently that between direct
and indirect evidence, turn on whether the inference is a conscious and
readily distinguishable part of the judgment or not. Though bringing to
light an unconscious inference is often an essential part of the
detection of false reasoning, where there is no such practical
consequence, we need not be too curious here about the line between
direct observation and inference from observation. For the rough and
ready purposes of everyday arguments it is exact enough to say that
where you recognize that you are basing your conclusion as to a fact on
some process of reasoning, then you are resting on indirect evidence;
where you do not recognize the inference without reflection, you are
resting on direct evidence.
In the following discussion of reasoning I shall sometimes be dealing
with proving a fact, sometimes with arguing forward to a policy. In many
cases the two processes are practically identical, for if the fact is
established the policy follows as a matter of course: in these cases,
therefore, for the sake of convenience I shall use the terms
interchangeably, and keep them separate only where there is danger of
confusion.
33. Reasoning. Though the various forms of reasoning and the
principles which they follow are the concern rather of psychology and
logic than of a practical work on the writing of arguments, yet these
sciences help us to understand the processes of the mind by which we
convince first ourselves, and then other people, of the existence of
facts, when for one reason or another direct testimony is wanting.
Psychology describes the processes of reasoning as part of the activity
of the mind, analyzes them into their parts, and shows their working.
Logic is concerned rather with the forms of reasoning: its aim is to
establish principles and rules the application of which will insure
correct reasoning.
I shall first briefly and very simply sketch the underlying nature of
the reasoning process as it is described by psychologists; then I shall
pass on to a practical application of the principles thereby attained;
next I shall set forth a few of the simplest and clearest of the
processes of reasoning which have been worked out by logic; and,
finally, I shall discuss each few of the best-recognized forms of false
reasoning. From both the psychological description and the rules of
logic we shall derive practical suggestions for establishing facts
which may be needed in an argument.
The essential feature of the process of reasoning is that it proceeds
from like to like, by breaking up whole facts and phenomena,
and following out the implications or consequences of one
or more of the parts.[24] For example, if I infer, when my dog
comes out of a barnyard with an apologetic air, and with blood and
feathers on his mouth, that he has been killing a hen, I am breaking
up the whole phenomenon of the dog's appearance, and paying
attention only to the blood and feathers on his head; and
these lead me directly to similar appearances when I have caught
him in the act. If I reason, Every student who can concentrate his
attention can learn quickly, George Marston has a notable power
of concentration, Therefore George Marston can learn quickly, I
again break up the abstraction _student_, and the concrete fact
_George Marston_, and pay attention in each to the single characteristic,
_concentration of attention_. Thus by means of these similar
parts of different wholes I pass from the assertion concerning the
class as a whole to the assertion concerning the concrete case.
This process first of analysis and then of abstraction of similars is
the essential part of every act of reasoning.
In intuitive or unreasoned judgment, on the other hand, we
jump to the conclusion without analyzing the intermediate steps.
If I say, _I have a feeling in my bones that it will rain to-morrow,_
or, _it is borne in on me that our team will win_, the sensations and
ideas that I thus lump together are too subtle and too complex for
analysis, and the conclusion, though it may prove sound, is not
arrived at by reasoning. The difference between such intuitive
and unreasoned judgments, and reasoning properly so called, lies
in the absence or the presence of the intermediate step by which
we consciously recognize and choose out some single attribute or
characteristic of the fact or facts we are considering, and pass
from that to other cases in which it occurs.
The skill of the reasoner therefore consists of two parts: first, the
sagacity to pick out of the complex fact before him, the attribute or
characteristic which is significant for his present purpose; and second,
the large knowledge of the subject which will enable him to follow it
into other cases in which it occurs with different circumstances, or, in
other words, to follow a similarity through diverse cases. Darwin's
great achievement in establishing the principle of evolution lay first
in the scientific sagacity which flashed home on him, after years of
patient study, that the one common fact in all the multitude of plants
and animals is that in the struggle for existence by which all living
beings persist, those who are best fitted to their circumstances
survive; and second, in his rich knowledge of the world of nature, which
made it possible for him to follow out this characteristic in all kinds
of plants and animals, and so to reach the general law. But whether it
be so world-sweeping a conclusion as his, or my conclusion that my dog
has killed a hen, the process is the same: analysis or breaking up of
the complex fact, and following out the consequences or implications of
some selected part of it into other cases.
All reasoning thus reduces itself in the end to a process of passing
from like to like: we notice that the present case is like other cases
which we already know: then, since these cases have always in the past
been accompanied by certain circumstances or consequences, we believe
that the present case will also show these same circumstances or
consequences. Whenever my dog has killed when the cases have been
similar in the blood and feathers on his mouth; in this case he has
blood and feathers on his mouth; therefore he must have killed a hen.
Individual plants and animals survive which are fitted to their
environment by special characteristics, and those which are not so
fitted die; species of plants and animals, as well as individuals, show
special adaptation to their environment; therefore species have survived
through the same process of natural selection.
It follows that reasoning, whether it results in a general law or in
concrete judgment, depends on the assumption that nature--and in nature
we mean here the whole universe as we know it is uniform; that there are
ties between facts which make it possible for us to be certain that if a
given fact occurs, then another fact always occurs with it as an effect,
or as a cause, or connected with it in some other manner. Without this
certainty of the uniformity of things there would be no reasoning, and
therefore no argument from indirect evidence. Huxley sets forth this
fundamental truth clearly and impressively at the beginning of the first
of his "Lectures on Evolution" (see p. 234).
For practical purposes the various types of this inference from
similarity can be conveniently thrown into three groups. As will be
obvious, there is no fixed and impassable line between them.
"If an inference relies upon a resemblance that is newly seen, rare, or
doubtful, it is called an inference from analogy; if it is made upon the
basis of an established classification, it is called a generalization;
if it involves a variety of resemblances so combined as to bear upon a
single point, it is usually or frequently called an inference from
circumstantial evidence."[25]
I will take up each of these types and show how we use them in the
practical work of argument. It will be seen that they vary greatly in
certainty of results.
34. Reasoning from Analogy. Analogy in its most tenuous form is
weak as a basis for an actual inference, though it is often effective as
a means of expressing an intuitive judgment where the reasons are too
subtle and diffused for formal explanation. When Lincoln in the middle
of the Civil War said that men do not swap horses while they are
crossing a stream, the analog, though subtle, was felt to be real.
Popular adages and proverbs are common modes of expressing such
deep-lying analogies: for example, "Where there is smoke there is fire";
"The slothful man saith, There is a lion in the way." Poetry too is full
of these subtle, pregnant similarities which link things in some one
aspect, but fail for all others.
To die; to sleep;
No more; and by a sleep to say we end
The heart-ache and the thousand natural shocks
That flesh is heir to. 'Tis a consummation
Devoutly to be wish'd. To die; to sleep;--
To sleep? Perchance to dream! Ay, there's the rub;
For in that sleep of death what dreams may come,
When we have shuffl'd off this mortal coil,
Must give us pause.
But, as in this case of Hamlet's, poetical analogies will not bear much
strain; the aspect in which the similarity holds is usually the only
aspect the two cases have in common, and to take poetry as a precise
formulation of fact is to sin against both humor and sound reasoning.
In daily life we are constantly reasoning by analogy. If you argue that
a certain man who has been successful at the head of a railroad will
therefore make a good president for a college because that also is a
complex institution, or that because self-government has worked well in
a certain school it will probably work well in a college, or that
because a friend has been cured of sleeplessness by taking a walk just
before going to bed therefore everybody who sleeps badly can be cured in
the same way,--in all these cases you are reasoning by analogy. In each
case it will be noticed you would pass from a similarity which exists in
a single case or in a small number of cases to the conclusion. The
reasoning is sound, however, only in so far as the similarity bears on
the actual purpose in hand: in the first example, if the success of the
railroad president arises from the power of understanding men and of
philosophic insight into large problems, the reasoning will probably be
valid; in the last example, if applied to insomnia due to overwork, it
might be bad.
In practical affairs it is easy to find examples of reasoning from
analogy, especially in arguments of policy. The first trial of city
government by commission depended on such reasoning: when Galveston,
Texas, was devastated by a storm it was reasoned that in business
matters a small body of picked men with absolute powers are most
efficient in an emergency, and that since the reconstruction of the city
was essentially a matter of business, such a body would best meet the
emergency. So the extension of commission government in other states at
first followed reasoning by analogy: government by commission worked
well in Galveston; it would probably work well in Des Moines. In the
same way with the arguments for a parcels post: they proceed from the
analogy of the present postal service, which has been successful so far
as it goes, and from the success of the parcels post in almost all the
countries of Europe. If you were arguing that "Association" (or
"soccer") football should be made one of the major sports at your
college, you would reason from the analogy of its great popularity with
Englishmen all over the world that it would also probably be popular in
America.
When you use the argument from analogy, however, you must make sure that
the similarity between the two cases runs to the point you wish to
establish. In the following extract from an argument in favor of
commission government for all cities, the author explicitly limits his
reasoning from the analogy of Washington to the point of the extension
of the system to large cities.
If we look for successful governments by commission in this
country, it is not difficult to find them in our largest cities. The
city of Washington is governed by a small commission, and is
acknowledged to be one of our best-governed cities. While this
commission originated in an entirely different way from that of the
commission form of government, successful administration under its rule
is a valid answer to the argument that small commissions are suited only
to the administration of small cities.[26]
Whenever you use this type of reasoning, it is wise thus to limit its
bearing. If in an argument in favor of allowing secret societies in a
high school you rely on the analogy of college life, take pains to show
that the resemblance covers the social life of a school. If you were
arguing that your city should establish a municipal gymnasium, and
relied on the reasoning from the analogy of a family, in which all the
members have a direct interest in the health of the others, show that
this interest has practical grounds of welfare, and does not rest wholly
on affection. In every case, unless the limits of the analogy are
obvious, specify them in order to carry your readers safely with you.
35. False Analogy. A peculiar danger of the argument from analogy
is the fallacy which is known as false analogy, or reasoning to a
conclusion which the similarity does not support. Arguments in which
there are many figures of speech, especially when the style is at all
florid, are apt to slop over into this fallacy. To liken education to
the unfolding of a flower is all very well, if you do not go on to argue
that because the lily of the field neither toils nor spins, therefore a
child should do no work in school. It is said that M. Stolypin, the
late premier of Russia, once half apologized In the Duma for the
slowness of his reforms, saying that he Was like a man shooting with a
flintlock musket; to which one of the Liberal members replied that it
was not a question of weapons, but of aim, and that if his Excellency
was to go on shooting at the people, it would be better if he went on
using flintlocks. Under the auspices of the Carnegie Institution an
expert in business administration made an inquiry into the methods of
teaching and research in physics at various American universities, and
made recommendations based on the conduct of business establishments. A
professor of physics in answer showed in how many ways the analogy
between a business concern, whose end is profit, and a physical
laboratory, whose end is the advancement of knowledge, is false and
misleading. The expert had suggested a general research board to
correlate researches; the professor cited the cases of Airy, the
astronomer royal of England, who by his dominating position held back
astronomical research in England for a generation, and of Sir Humphry
Davy, who discouraged the work of Faraday, when the latter was his
assistant.
The expert suggested that apparatus could be passed on from
one investigator to another: the professor replied that few men can use
apparatus designed for some one else's purpose, and that the cost of
reconstruction would exceed the cost of new machines. In short, he
completely riddled the argument from analogy set up by the expert.[27]
A notable example of conclusive refutation of an argument based on a
false analogy is to be found in William James's Ingersoll Lecture on
Immortality. He took up the ordinary argument against the immortality of
the soul, which, starting from the accepted physiological and
psychological formula, "Thought is a function of the brain," reasons
that therefore when the brain dies and decays, thought and consciousness
die, too.
This, then, is the objection to immortality; and the next thing in
order for me is to try to make plain to you why I believe that it has in
strict logic no deterrent power. I must show you that the fatal
consequence is not coercive, as is commonly imagined; and that, even
though our soul's life (as here below it is revealed to us) may be in
literal strictness the function of a brain that perishes, yet it is not
at all impossible, but on the contrary quite possible, that the life may
still continue when the brain itself is dead.
The supposed impossibility of its continuing comes from too superficial
a look at the admitted fact of functional dependence. The moment we
inquire more closely into the notion of functional dependence, and ask
ourselves, for example, how many kinds of functional dependence there
may be, we immediately perceive that there is one kind at least that
does not exclude a life hereafter at all. The fatal conclusion of the
physiologist flows from his assuming offhand another kind of functional
dependence, and treating it as the only imaginable kind.
When the physiologist who thinks that his science cuts off all hope of
immortality pronounces the phrase, "Thought is a function of the brain,"
he thinks of the matter just as he thinks when he says, "Steam is a
function of the teakettle," "Light is a function of the electric
circuit," "Power is a function of the moving waterfall." In these latter
cases the several material objects have the function of inwardly
creating or engendering their effects, and their function must be called
_productive_ function. Just so, he thinks, it must be with the brain.
Engendering consciousness in its interior, much as it engenders
cholesterin and creatin and carbonic acid, its relation to our soul's
life must also be called productive function. Of course, if such
production be the function, then when the organ perishes, since the
production can no longer continue, the soul must surely die. Such a
conclusion as this is indeed inevitable from that particular conception
of the facts.
Rut in the world of physical nature productive function of this sort is
not the only kind of function with which we are familiar. We have also
releasing or permissive function; and we have transmissive function.
The trigger of a crossbow has a releasing function: it removes the
obstacle that holds the string, and lets the bow fly back to its natural
shape. So when the hammer falls upon a detonating compound. By knocking
out the inner molecular obstructions, it lets the constituent gases
resume their normal bulk, and so permits the explosion to take place.
In the case of a colored glass, a prism, or a refracting lens, we have
transmissive function. The energy of the light, no matter how produced,
is by the glass sifted and limited in color, and by the lens or prism
determined to a certain path and shape. Similarly, the keys of an organ
have only a transmissive function. They open successively the various
pipes and let the wind in the air chest escape in various ways. The
voices of the various pipes are constituted by the columns of air
trembling as they emerge. But the air is not engendered in the organ.
The organ proper, as distinguished from its air chest, is only an
apparatus for letting portions of It loose upon the world in these
peculiarly limited shapes.
My thesis now is this: that, when we think of the law that thought is a
function of the brain, we are not required to think of productive
function only; _we are entitled also to consider permissive or
transmissive function_. And this the ordinary psychophysiologist leaves
out of account.[28]
The question of the validity of an analogy in reasoning is always, as
here, whether the similarity on which the reasoning rests really runs
between the two cases in hand, or is not merely a general resemblance
expressed by some phrase or word which seems to mean more than it does.
In other words, when you are testing an analogy, whether your own or an
opponent's, make sure that the similarity is real for the present case.
A picturesque figure of speech may add life to an argument, but it may
also cover a gap in the reasoning.
36. Reasoning by Classification or Generalization. Obviously the
strength of reasoning from analogy increases with the number of cases
which you can point to as showing the similarity on which you rely, for
you can then begin to generalize and classify.
Analogy expresses our natural tendency to assimilate the new to the old,
to interpret what is strange and unfamiliar in the light of what we
already know. It may therefore be described as classification in the
making. The resemblances which guide us are called analogies so long as
they are newly seen, rare, or doubtful; but as the number of cases
increases, analogy passes by insensible stages into established
classification.[29]
An excellent example of this transition may be seen in the present state
of the argument in favor of commission government: at first, as we have
seen, it depended chiefly on reasoning from analogy; by this time enough
cities have adopted the plan to make it possible to classify them, and
so reason by generalization.
Generalization and classification, it may be noted in passing, are two
aspects of the same process of thought. When one passes from the
individual facts to the larger fact which brings them together, as in
the assertion, _Members of the Phi Beta Kappa are good scholars_, one
makes a generalization; when one asserts of an individual the larger
fact, as in the assertion, My _brother is a good scholar_ (My _brother
belongs to the class Good Scholars_), one makes a classification.
When a classification or generalization is constant and familiar, it
brings forth, by the natural economy of language, a name for the class
or the principle; "federation," "deciduous trees," "emotion," "terminal
moraine," are all names of classes; "attraction of gravity," "erosion,"
"degeneration," "natural selection," are names of principles which sum
up acts of generalization. Almost always these names begin as figures of
speech, but where they are used accurately they have a perfectly exact
meaning. Darwin has given some account of this process of language:
"It has been said that I speak of natural selection as an active power
or deity, but who objects to an author speaking of the attraction of
gravity as ruling the movements of planets? Every one knows what is
meant by such metaphorical expressions, and they are almost necessary
for brevity: so, again, it is difficult to avoid personifying the word
'Nature.' But I mean by Nature the aggregate action and product of many
laws, and by laws the sequence of events as ascertained by us."[30]
When the facts intended to be meant by a phrase are thus carefully
specified and delimited, the phrase ceases to be a figure of speech, and
becomes the name of a class or of a principle.
Generalization and classification always take place for purposes of
reasoning;[31] and reasoning which is dependent on them rests on the
assumption that things are uniformly correlated in nature; when we
throw things together into classes we assume that what is true for one
member of a class, so far as it is a member of that class, is true to
the same extent and for the purpose for which the class is made for all
other members of that class.
In practice a large part of our reasoning is through generalization and
classification; and as we have seen, it has a more substantial basis
than when we rest on an analogy. If you hear that your brother has been
elected to the Phi Beta Kappa, you reason from the generalization that
all members of the Phi Beta Kappa are high scholars to the inference
that your brother must have taken high rank. When I see a gang of
carpenters knocking off work at four o'clock in the afternoon, I infer
that they must belong to the union, because I know that unions as a
class have established an eight-hour day. If you were arguing that the
standards for graduation from your college should be raised, you would
try to show that each year enough men are graduated with low
intellectual attainments to make a class large enough to generalize
from. If you were arguing that your city should establish a municipal
gymnasium, you would try to show that of the boys and young men brought
before the police courts for petty mischief and more serious offenses
almost all have lacked the chance to work off their animal spirits in a
healthy way. Wherever you can thus establish your special case in a
class which has known characteristics or consequences, you can then
apply the characteristics and consequences of the class to your special
case.
Where the class is recognized as having definite characteristics or
consequences, you can make your inference by showing that your case
falls within the class. Sometimes the stress of your reasoning will come
on making it clear that the consequence or characteristic on which your
reasoning depends really belongs to the class. If, for example, you were
arguing, as did the Class of '85 at Amherst College, that your college
should return to something like the old-fashioned classical education,
you would try to establish the fact that men who have had the
old-fashioned classical education are as a rule characterized by
intelligence, liberal culture, and open-mindedness. In such cases it is
the generalization on which the class is based which is the difficult
part of your task.
In general, however, if you can show your readers that the present case
belongs in a class of cases which can be recognized as belonging
together by virtue of definable characteristics, you have established an
excellent foundation for an inference based on those characteristics.
37. Reasoning by Causal Relation. Reasoning by generalization rises
greatly in certainty, however, whenever you can show the workings of
cause and effect. If a college receives every year from a certain school
a number of boys who are slack and lazy students, the dean of that
college may come to generalize and expect most of the boys from that
school to be poor timber. If, however, he finds that the master of the
school will take and keep any boy who lives in the town, he is able to
argue from this as a cause to the conclusion that the standards of the
school are low, and then from these low standards as a cause to the poor
quality of the graduates of the school.
Here is another example, from Professor James:
I am sitting in a railroad car, waiting for the train to start. It
is winter, and the stove fills the car with pungent smoke. The
brakeman enters, and my neighbor asks him to "stop that stove
smoking." He replies that it will stop entirely as soon as the car
begins to move. "Why so?" asks the passenger. "It _always_ does,"
replies the brakeman. It is evident from this "always" that the
connection between car moving and smoke stopping was a purely
empirical one in the brakeman's mind, bred of habit. But if the
passenger had been an acute reasoner ... [and had] singled out of
all the numerous points involved in a stove's not smoking the one
special point of smoke pouring freely out of the stove-pipe's mouth,
he would probably ... have been immediately reminded of the law that
a fluid passes more rapidly out of a pipe's mouth if another fluid
be at the same time streaming over that mouth.[32]
Here the passenger's certainty that the smoking would stop would have
been much increased if he had, as Professor James suggests, reasoned to
the cause, instead of trusting to the brakeman's generalization from
experience.
In scientific matters search for cause and effect the chief mode of
progress. General Sternberg's article "Yellow Fever and Mosquitoes"
(p. 251) is an admirable account of this advance from probability to
certainty, which comes from demonstrating the necessary sequence which
we call cause and effect. When Major Reed and his associates had shown
that in cases where mosquitoes were kept away there was no yellow fever,
but that in cases where infected mosquitoes were allowed to bite
patients yellow fever followed, they turned the probability that
mosquitoes were the transmitting agent of the fever into a certainty.
Likewise with the glacial theory: it had already in the time of the
elder Professor Agassiz been established that certain regions of
northern Europe and America could be classed together by the occurrence
of certain phenomena--rounded hills, ledges of rock smoothed off and
marked with scratches running more or less north and south, deposits of
clean gravel and sand, boulders of various foreign kinds of rock
scattered over the surface of the country; when he showed that glaciers
in their movements produce all these phenomena, he laid bare the cause
of the phenomena, and so demonstrated with practical certainty the
theory of the former existence of a huge glacial sheet in the northern
hemisphere. Wherever you can show that your case not only belongs to a
recognized class of cases, with recognized characteristics, but also
that in those characteristics there is a necessary sequence of cause and
effect, you have proved your point.
In the example above, of an argument for the establishment of a
municipal gymnasium, if after showing that all the boys and young men
who get into the courts have no normal and healthy way of working off
their natural animal spirits, you can show that in places where through
settlements or municipal action gymnasiums have been provided, the
number of arrests of boys and young men has greatly fallen off, you have
established the grounds for an inference of cause and effect which gives
your argument a wholly new strength. In the case of the argument for a
return to a classical course in a college, this sequence of cause and
effect would be very difficult to establish, for here you would be deep
down in the most complex and subtle region of human nature. Wherever it
is possible, however, lead the inference from a classification or
generalization on to an inference of cause and effect.
38. Induction and Deduction. Our next step is to consider how we
get the generalizations on which we base so much of our reasoning. As we
have seen, the science which deals with the making of them, with their
basis, and with the rules which govern inferences made from them is
logic.
Logicians generally distinguish between two branches of their science,
inductive and deductive reasoning. In inductive reasoning we pass from
individual facts to general principles; in deductive reasoning we pass
from general principles to conclusions about individual facts. The
distinction, however, draws less interest in recent times than formerly,
and logicians of the present generation tend to doubt whether it has any
vital significance.[33] They point out that in practice we
intermingle the two kinds almost inextricably, that the distinction
between facts and principles is temporary and shifting, and that we
cannot fit some of the common forms of inference into these categories
without difficult and complicated restatement.
Nevertheless, as deductive logic and inductive logic are ancient and
time-honored terms which have become a part of the vocabulary of
educated men, it is worth while to take some note of the distinction
between them, I shall not attempt here to do more than to explain a few
of the more important principles. I shall begin with inductive logic,
since that is the branch which deals with the making of generalizations
from individual fact, and therefore that which has most concern in the
arguments of the average man in his passage through life.
39. Inductive Reasoning. In inductive reasoning we put individual
facts and cases together into a class on the basis of some definable
similarity, and then infer from them a general principle. The types of
inductive reasoning have been reduced by logicians to certain canons,
but these reduce themselves to two main methods, which depend on whether
in a given piece of reasoning we start from the likeness between the
instances or the differences between them. On these two methods, the
method of agreement and the method of difference, hang all the processes
of modern science, and most of our everyday arguments.
The method of agreement has been defined as follows:
If two or more instances of the phenomenon under investigation have
only one circumstance in common, the circumstance in which alone all the
instances agree is the cause (or effect) of the given phenomenon.[34]
A few examples, which might easily be multiplied, will show how
constantly we use this method in everyday life. Suppose that a teacher
is annoyed at somewhat irregular intervals by whispering and laughing in
the back of the schoolroom, for which he can find no cause, but that
presently he notices that whenever a certain pair of boys sit together
there the trouble begins; he infers that these two boys are the cause of
the trouble.
In the old days before it had been discovered that the germs of malaria
are carried by mosquitoes, the disease was ascribed to a miasma which
floated over low ground at night; and the innkeepers of the Roman
Campagna, where malaria had almost driven out the population, urged
their guests never to leave their windows open at night, for fear of
letting in the miasma. In the lights of those days this was good
reasoning by the method of agreement, for it was common observation that
of all the many kinds of people who slept with their windows open most
had malaria. We are constantly using this method in cases of this sort,
where from observation we are sure that a single cause is at work under
diverse circumstances. If the cases are numerous enough and diverse
enough, we arrive at a safe degree of certainty for practical purposes.
As the case just cited shows, however, the method does not establish a
cause with great certainty. No matter how many cases we gather, if a
whole new field related to the subject happens to be opened up, the
agreement may be shattered.
The method of difference, which in some cases does establish causes with
as great certainty as is possible for human fallibility, works in the
opposite way: instead of collecting a large number of cases and noting
the single point of agreement, it takes a single case and varies a
single one of its elements. The method has been stated as follows:
If an instance in which the phenomenon occurs, and an instance in which
it does not occur, have every circumstance in common save one, that one
occurring only in the former; the circumstance in which alone the two
instances differ, is the effect, or the cause, or an indispensable part
of the cause, of the phenomenon.[35]
The principle is clearer and more apprehensible in the concrete example
than in the abstract statement; as a matter of fact it is applied in
every experimental search for a cause. The Agricultural College of New
York, for example, in the course of certain experiments on apple
orchards, bought an orchard which had not been yielding well, and
divided it into halves; one half was then kept plowed and cultivated,
the other half was left in grass; otherwise the treatment was the same.
When the half which was kept cultivated gave a much larger yield than
the other, it was safe to infer that the cultivation was the cause of
the heavier yield. Dr. Ehrlich, the great German pathologist, is said to
have tried six hundred and five different substances before he found one
which would kill the germ of a certain disease; in each experiment he
was using the method of difference, keeping the conditions the same in
all except a single point, which was the addition of the substance used
in that particular experiment. Wherever the conditions of an experiment
can be thus controlled, the method of difference gives a very accurate
way of discovering causes. With advancing knowledge a supposed cause may
be in turn analyzed in such a way that each of its parts can be
separately varied, in order to come more closely to the actual sequence
involved.