EVIDENCE
After you have marshaled the facts you wish to prove, you must consider
the classes of evidence by which you wish to prove them.
In the first place there is the direct statement of the facts by
witnesses, or the opinions of those witnesses who are qualified to speak
as experts. Then there is circumstantial evidence, which consists of
inferences fairly drawn from facts; in other words reasoning about facts.
Thus if you wish to prove that cutting the forest off the northern part
of the lower peninsula of Michigan has lessened the rainfall in that
State, you could present three classes of testimony. You could bring
forward an old resident who had known Michigan when it was wooded and
when it was stripped of its timber; if from his own personal observation
he could testify that as the timber was cut off the rainfall had
diminished, that would be direct evidence of that fact. If you presented
the statements of a scientist who would testify that when lands were
stripped of their trees, there was less rainfall, his opinions would be
entitled to consideration as proof of the facts just in the proportion
that his observation and experience had been extended and at the same
time exact.
=Circumstantial Evidence.=—If the cutting of the forests in Minnesota
near the head waters of the Mississippi was under discussion, you might
present the testimony of a man who lived on the banks of that river
in Iowa, who had never seen Minnesota, but who could testify that the
volume of water in the river had decreased from year to year in certain
proportion. His testimony would be valuable as tending to establish
your position, if you could also show that the cutting of the timber in
Minnesota had proceeded in the same ratio as the decrease in the river’s
volume. It would then be a fair inference that the two facts were so
connected that one tended to prove the other.
The line, however, between direct and circumstantial evidence is very
faint—one imperceptibly glides into the other. Indeed some experts insist
that there is no such thing as direct evidence. They urge that all proof
consists of deductions which may be so closely related to the fact to be
established that a mere statement conclusively shows the causal relation.
On the other hand this relation can frequently be shown only by the most
delicate fitting together of all the links of circumstance. For example,
suppose the testimony of A is that he saw B point a gun at C, that the
gun was fired, that immediately C fell dead. His testimony would be,
therefore, that B shot C and you, if you were on the jury, would perhaps
feel justified in finding B guilty of murder—there would seem to be no
doubt about it. But after all, his testimony is not direct evidence—even
as simple and apparently as conclusive a statement as his might be
explained away. Suppose, for example, an autopsy showed that C had heart
disease and fell dead from that cause, and that the bullet penetrated
C’s arm only. What to the observer would seem like irrefutable proof
would be dissipated in a moment; it would be shown to be an unwarrantable
deduction from certain circumstances.
Remember, however, that the value of evidence is in this ratio: that
direct evidence of a witness who knows of his own knowledge and
observation in the particular case is more to be trusted than expert
evidence based on general observation, and that both are worth more than
that evidence which is the result of deduction and inference.
=Qualifications of Witnesses.=—In weighing the value of the testimony
offered to prove your facts—testimony is those statements of the witness
which make up his evidence—you must ask him certain questions. If he were
a witness in a law suit, the lawyers would bring out the points you must
determine by four questions. Following their example, you will first ask
“Is he honest or prejudiced?” In the conservation question considered,
you would ask whether he was the agent of a lumber company whose
statements would naturally be influenced by his selfish interest, or a
homesteader who, since his only use for land was for farming purposes,
would likely be as prejudiced the other way, or was he a banker or
merchant who served both classes equally, whose interest lay equally with
each party to the controversy?
You will next ask if his testimony is consistent with known facts. If he
testified that the absence of trees had nothing to do with rainfall and
had cited as proof of that alleged fact that there was a heavy rainfall
in Sahara where there were no trees, you could at once dismiss him as an
impossible witness because his statements as to Sahara were inconsistent
with the known facts.
You should then inquire under what circumstances were the statements
made: were they forced from him, were his relations such that he was a
voluntary and willing witness endeavoring to assist investigation and
find out the facts? If so, his testimony is probably valuable and worthy
of credence.
Then in the last place, if the statements are made as those of an expert,
the value of his testimony is in the exact ratio of his experience in the
particular field discussed. Here is the opportunity for a very common
error in argument. Frank in debating might have urged the opinion of
Professor A or Doctor B, and Jack in his reply urged confidently the
opinions of Judge C or General D as disposing of the evidence of Frank’s
witnesses. But they would simply offset one opinion with another unless
Jack could show that the judge and the general knew more about the
subject matter than the professor and the doctor. Character or standing
or position would avail nothing. In discussing conservation, for example,
the opinion of the most eminent professor in a theological school or
the greatest expert in _running electric cars_ would not be received in
questions of soil moisture or timber culture. It is not the standing of
the man generally; it is his knowledge of the subject discussed, which
makes his opinions acceptable as evidence. The evidence of a farmer or
hunter or trapper, although unable to read or write, might outweigh that
of the so-called expert.
=Generalizations.=—Next, in weighing circumstantial evidence, you will
observe that there are three common forms in which it appears. There is
first the generalization—very frequently the shape an expert’s opinion
takes. If he says that timber tracts are worth so many dollars an acre
as timber and so many dollars an acre as farms, his opinion is valuable
or not depending upon what the basis of his judgment is. If it develops
that he has observed many hundreds of such tracts of land, and that these
different tracts lay in many different places, you safely conclude that
his testimony, although a generalization, is sound because it is based
upon wide observation. If he has inspected but very few such tracts, you
conclude that his generalization is unsound, and worthless in helping you
prove the facts.
Do not hesitate to apply the probe to the qualifications of your
opponent’s expert, but be equally sure you establish the right of your
own witness to speak as such. For example, I remember a case where the
question involved was whether dehorning cattle was cruel within the
meaning of a statute forbidding cruelty to animals. One side brought
forward as expert professional witnesses certain surgeons eminent in
their profession. They testified that the horn of the cow contained just
under the hard bony shell a thin membranous structure, the extension of
the periosteum, which was very sensitive to pain. They testified that
they had known of cases where the shell of the horn had been removed
by accident and this membrane exposed, whereupon the animals had given
every manifestation of suffering excruciating pain. They argued from the
sensitiveness of the periosteum, through these few instances of accident,
to the deduction that dehorning cows, that is, sawing the horn off at
right angles to this membrane, must also be extremely painful and hence
cruel.
Opposed to these expert opinions of these surgeons based upon these few
cases, were the opinions of farmers who did not pretend to have the
scientific knowledge of the surgeons but who _had dehorned many cows_.
They testified that they had seen but slight evidences of pain, that the
animals had shown annoyance rather than distress, and had generally at
once gone to eating. The farmers had no titles or university degrees; the
experts had both, and supposedly in the very field of the debate—for that
was what it was, although in a court of law. The superior qualifications
of the plain unlettered farmers made their evidence of much greater value
as expert testimony than the deductions of the expert gentlemen from the
city.
Suppose you are discussing the adoption of a law prohibiting child labor.
You can quote with confidence the opinion of a social worker whose daily
duties keep her among operatives in mills. By her daily observation she
is in a position to know the evil effects of labor on immature bodies and
minds. So is the doctor or the teacher who sees these children daily. On
the other hand, the farmer, who, although honest in his deduction from
the results of his own labor, is not qualified because he himself worked
as a boy on a farm to speak understandingly of the effects of child labor
in mills or factories. He must confine his testimony to the effect of
child labor on the farm. Nor is the woman who knows nothing of labor on
farm or in factory qualified to speak at all, sentimentally aroused as
she may be, unless she can show observation of conditions herself or the
intelligent study of the well founded opinions of others.
=Cause and Effect.=—Then again there is in circumstantial evidence the
inference you draw from the relation of cause and effect. To use a very
familiar example: Suppose you pass a piece of ground where to your
knowledge there stood but a very few weeks before a heavy growth of
timber and observe that the trees are gone. If you see piles of freshly
sawed lumber, you can argue that the trees have been cut by man; if on
the other hand you see bent and torn trees, you can as surely reason
that a cyclone has visited that neighborhood. In each case you argue
from effect back to cause. This seems very simple, but is often a very
treacherous argument, for the alleged cause may be entirely inadequate or
may be so involved with other unrecognized causes that the deduction you
make is not warranted. You must examine the connection very carefully and
make sure that it is a CAUSAL relation and not a CASUAL one.
=Argument from Resemblance.=—Then there is the argument from resemblance,
which is simply another form of causal relationship. The argument, for
example, would run that conservation must surely be a good thing for
the United States because it was a good thing for New Zealand. That
conclusion is sound if the conditions in the two countries are the same,
but not otherwise; and it is upon this rock of difference in conditions
that arguments from resemblance so often split. Watch them. The same
rule may not apply to reforestration in Idaho as in Maine, for instance,
because conditions are dissimilar in many respects.
If you carefully study these forms of argument, and can estimate the
value of opinions and circumstantial evidence, you will not only be able
to build up a bomb proof argument of your own but you will be able to
detect fallacies in your opponent’s discussion. When you have mastered
the one branch of the case you are equipped to meet the other, for the
two are identical.