we are confronted by an initial and insuperable difficulty. Aristotle
is always anxious to insist on the difference between his own doctrines
and those of Plato, and his bias in this direction regularly leads him
to speak as though he held a thorough-going naturalistic and empirical
theory with no "transcendental moonshine" about it. Yet his final
conclusions on all points of importance are hardly distinguishable from
those of Plato except by the fact that, as they are so much at variance
with the naturalistic side of his philosophy, they have the appearance
of being sudden lapses into an alogical mysticism. We shall find the
presence of this "fault" more pronouncedly in his metaphysics,
psychology, and ethics than in his theory of knowledge, but it is not
absent from any part of his philosophy. He is everywhere a Platonist
_malgre lui_, and it is just the Platonic element in his thought to
which it owes its hold over men's minds.
Plato's doctrine on the subject may be stated with enough accuracy for
our purpose as follows. There is a radical distinction between
sense-perception and scientific knowledge. A scientific truth is exact
and definite, it is also true once and for all, and never becomes truer
or falser with the lapse of time. This is the character of the
propositions of the science which Plato regarded as the type of what
true science ought to be, pure mathematics. It is very different with
the judgments which we try to base on our sense-perceptions of the
visible and tangible world. The colours, tastes, shapes of sensible
things seem different to different percipients, and moreover they are
constantly changing in incalculable ways. We can never be certain that
two lines which seem to our senses to be equal are really so; it may be
that the inequality is merely too slight to be perceptible to our
senses. No figure which we can draw and see actually has the exact
properties ascribed by the mathematician to a circle or a square. Hence
Plato concludes that if the word science be taken in its fullest sense,
there can be no science about the world which our senses reveal. We can
have only an approximate knowledge, a knowledge which is after all, at
best, probable opinion. The objects of which the mathematician has
certain, exact, and final knowledge cannot be anything which the senses
reveal. They are objects of _thought_, and the function of visible
models and diagrams in mathematics is not to present _examples_ of them
to us, but only to show us imperfect _approximations_ to them and so to
"remind" the soul of objects and relations between them which she has
never cognised with the bodily senses. Thus mathematical straightness
is never actually beheld, but when we see lines of less and more
approximate straightness we are "put in mind" of that absolute
straightness to which sense-perception only approximates. So in the
moral sciences, the various "virtues" are not presented in their
perfection by the course of daily life. We do not meet with men who are
perfectly brave or just, but the experience that one man is braver or
juster than another "calls into our mind" the thought of the absolute
standard of courage or justice implied in the conviction that one man
comes nearer to it than another, and it is these absolute standards
which are the real objects of our attention when we try to define the
terms by which we describe the moral life. This is the
"epistemological" side of the famous doctrine of the "Ideas." The main
points are two, (1) that strict science deals throughout with objects
and relations between objects which are of a purely intellectual or
conceptual order, no sense-data entering into their constitution; (2)
since the objects of science are of this character, it follows that the
"Idea" or "concept" or "universal" is not arrived at by any process of
"abstracting" from our experience of sensible things the features common
to them all. As the particular fact never actually exhibits the
"universal" except approximately, the "universal" cannot be simply
disentangled from particulars by abstraction. As Plato puts it, it is
"apart from" particulars, or, as we might reword his thought, the pure
concepts of science represent "upper limits" to which the comparative
series which we can form out of sensible data continually approximate
but do not reach them.
In his theory of knowledge Aristotle begins by brushing aside the
Platonic view. Science requires no such "Ideas," transcending
sense-experience, as Plato had spoken of; they are, in fact, no more
than "poetic metaphors." What is required for science is not that there
should be a "one over and above the many" (that is, such pure concepts,
unrealised in the world of actual perception, as Plato had spoken of),
but only that it should be possible to predicate one term universally of
many others. This, by itself, means that the "universal" is looked on
as a mere residue of the characteristics found in each member of a
group, got by abstraction, _i.e._ by leaving out of view the
characteristics which are peculiar to some of the group and retaining
only those which are common to all. If Aristotle had held consistently
to this point of view, his theory of knowledge would have been a purely
empirical one. He would have had to say that, since all the objects of
knowledge are particular facts given in sense-perception, the universal
laws of science are a mere convenient way of describing the observed
uniformities in the behaviour of sensible things. But, since it is
obvious that in pure mathematics we are not concerned with the actual
relations between sensible data or the actual ways in which they behave,
but with so-called "pure cases" or ideals to which the perceived world
only approximately conforms, he would also have had to say that the
propositions of mathematics are not strictly true. In modern times
consistent empiricists have said this, but it is not a position possible
to one who had passed twenty years in association with the
mathematicians of the Academy, and Aristotle's theory only begins in
naturalism to end in Platonism. We may condense its most striking
positions into the following statement. By science we mean _proved_
knowledge. And proved knowledge is always "mediated"; it is the
knowledge of _conclusions_ from premisses. A truth that is
scientifically known does not stand alone. The "proof" is simply the
pointing out of the connection between the truth we call the conclusion,
and other truths which we call the premisses of our demonstration.
Science points out the _reason why_ of things, and this is what is meant
by the Aristotelian principle that to have science is to know things
through their _causes_ or _reasons why_. In an ordered digest of
scientific truths, the proper arrangement is to begin with the simplest
and most widely extended principles and to reason down, through
successive inferences, to the most complex propositions, the _reason
why_ of which can only be exhibited by long chains of deductions. This
is the order of logical dependence, and is described by Aristotle as
reasoning _from_ what is "more knowable in its own nature,"[#] the
simple, to what is usually "more familiar to _us_," because less removed
from the infinite wealth of sense-perception, the complex. In
_discovery_ we have usually to reverse the process and argue from "the
familiar to us," highly complex facts, to "the more knowable in its own
nature," the simpler principles implied in the facts.
[#] This simple expression acquires a mysterious appearance in mediaeval
philosophy from the standing mistranslation _notiora naturae_, "better
known to nature."
It follows that Aristotle, after all, admits the disparateness of
sense-perception and scientific knowledge. Sense-perception of itself
never gives us scientific truth, because it can only assure us that a
fact is so; it cannot _explain_ the fact by showing its connection with
the rest of the system of facts, "it does not give the _reason_ for the
fact." Knowledge of perception is always "immediate," and for that very
reason is never scientific. If we stood on the moon and saw the earth,
interposing between us and the sun, we should still not have scientific
knowledge about the eclipse, because "we should still have to ask for
the _reason why_." (In fact, we should not know the reason _why_
without a theory of light including the proposition that light-waves are
propagated in straight lines and several others.) Similarly Aristotle
insists that Induction does not yield scientific truth. "He who makes
an induction points out something, but does not demonstrate anything."
For instance, if we know that _each_ species of animal which is without
a gall is long-lived, we may make the induction that _all_ animals
without a gall are long-lived, but in doing so we have got no nearer to
seeing _why_ or _how_ the absence of a gall makes for longevity. The
question which we may raise in science may all be reduced to four heads,
(1) Does this thing exist? (2) Does this event occur? (3) If the thing
exists, precisely what is it? and (4) If the event occurs, _why_ does it
occur? and science has not completed its task unless it can advance from
the solution of the first two questions to that of the latter two.
Science is no mere catalogue of things and events, it consists of
inquiries into the "real essences" and characteristics of things and the
laws of connection between events.
Looking at scientific reasoning, then, from the point of view of its
formal character, we may say that all science consists in the search for
"middle terms" of syllogisms, by which to connect the truth which
appears as a conclusion with the less complex truths which appear as the
premisses from which it is drawn. When we ask, "does such a thing
exist?" or "does such an event happen?" we are asking, "is there a
middle term which can connect the thing or event in question with the
rest of known reality?" Since it is a rule of the syllogism that the
middle term must be taken universally, at least once in the premisses,
the search for middle terms may also be described as the search for
universals, and we may speak of science as knowledge of the universal
interconnections between facts and events.
A science, then, may be analysed into three constituents. These are: (1)
a determinate class of objects which form the subject-matter of its
inquiries. In an orderly exhibition of the contents of the science,
these appear, as in Euclid, as the initial data about which the science
reasons; (2) a number of principles, postulates, and axioms, from which
our demonstrations must start. Some of these will be principles
employed in all scientific reasoning. Others will be specific to the
subject-matter with which a particular science is concerned; (3) certain
characteristics of the objects under study which can be shown by means
of our axioms and postulates to follow from our initial definitions, the
_accidentia per se_ of the objects defined. It is these last which are
expressed by the conclusions of scientific demonstration. We are said
to know scientifically that B is true of A when we show that this
follows, in virtue of the principles of some science, from the initial
definition of A. Thus if we convinced ourselves that the sum of the
angles of a plane triangle is equal to two right angles by measurement,
we could not be said to have scientific knowledge of the proposition.
But if we show that the same proposition follows from the definition of
a plane triangle by repeated applications of admitted axioms or
postulates of geometry, our knowledge is genuinely scientific. We now
know that it is so, and we see _why_ it is so; we see the connection of
this truth with the simple initial truths of geometry.
This leads us to the consideration of the most characteristic point of
Aristotle's whole theory. Science is demonstrated knowledge, that is,
it is the knowledge that certain truths follow from still simpler
truths. Hence the simplest of all the truths of any science cannot
themselves be capable of being known by inference. You cannot infer
that the axioms of geometry are true because its conclusions are true,
since the truth of the conclusions is itself a consequence of the truth
of the axioms. Nor yet must you ask for demonstration of the axioms as
consequences of still simpler premisses, because if all truths can be
proved, they ought to be proved, and you would therefore require an
infinity of successive demonstrations to prove anything whatever. But
under such conditions all knowledge of demonstrated truth would be
impossible. The first principles of any science must therefore be
indemonstrable. They must be known, as facts of sense-perception are
known, immediately and not mediately. How then do we come by our
knowledge of them? Aristotle's answer to this question appears at first
sight curiously contradictory. He seems to say that these simplest
truths are apprehended intuitively, or on inspection, as self-evident by
Intelligence or Mind. On the other hand, he also says that they are
known _to us_ as a result of induction from sense-experience. Thus he
_seems_ to be either a Platonist or an empiricist, according as you
choose to remember one set of his utterances or another, and this
apparent inconsistency has led to his authority being claimed in their
favour by thinkers of the most widely different types. But more careful
study will show that the seeming confusion is due to the fact that he
tries to combine in one statement his answers to two quite different
questions, (1) how we come to reflect on the axioms, (2) what evidence
there is for their truth. To the first question he replies, "by
induction from experience," and so far he might seem to be a precursor
of John Stuart Mill. Successive repetitions of the same
sense-perceptions give rise to a single experience, and it is by
reflection on experience that we become aware of the most ultimate
simple and universal principles. We might illustrate his point by
considering how the thought that two and two are four may be brought
before a child's mind. We might first take two apples, and two other
apples and set the child to count them. By repeating the process with
different apples we may teach the child to dissociate the result of the
counting from the particular apples employed, and to advance to the
thought, "any two apples and any two other apples make four apples."
Then we might substitute pears or cherries for the apples, so as to
suggest the thought, "two fruits and two fruits make four fruits." And
by similar methods we should in the end evoke the thought, "any two
objects whatever and any other two objects whatever make four objects."
This exactly illustrates Aristotle's conception of the function of
induction, or comparison of instances, in fixing attention on a
universal principle of which one had not been conscious before the
comparison was made.
Now comes in the point where Aristotle differs wholly from all
empiricists, later and earlier. Mill regards the instances produced in
the induction as having a double function; they not merely fix the
attention on the principle, they also are the evidence of its truth.
This gives rise to the greatest difficulty in his whole logical theory.
Induction by imperfect enumeration is pronounced to be (as it clearly
is) fallacious, yet the principle of the uniformity of Nature which Mill
regards as the ultimate premiss of all science, is itself supposed to be
proved by this radically fallacious method. Aristotle avoids a similar
inconsistency by holding that the sole function of the induction is to
fix our attention on a principle which it does not prove. He holds that
ultimate principles neither permit of nor require proof. When the
induction has done its work in calling attention to the principle, you
have to see for yourself that the principle is true. You see that it is
true by immediate inspection just as in sense-perception you have to see
that the colour before your eyes is red or blue. This is why Aristotle
holds that the knowledge of the principles of science is not itself
science (demonstrated knowledge), but what he calls intelligence, and we
may call intellectual intuition. Thus his doctrine is sharply
distinguished not only from empiricism (the doctrine that universal
principles are proved by particular facts), but also from all theories
of the Hegelian type which regard the principles and the facts as
somehow reciprocally proving each other, and from the doctrine of some
eminent modern logicians who hold that "self-evidence" is not required
in the ultimate principles of science, as we are only concerned in logic
with the question what consequences follow from our initial assumptions,
and not with the truth or falsehood of the assumptions themselves.
The result is that Aristotle does little more than repeat the Platonic
view of the nature of science. Science consists of deductions from
universal principles which sensible experience "suggests," but into
which, as they are apprehended by a purely intellectual inspection, no
sense-data enter as constituents. The apparent rejection of
"transcendental moonshine" has, after all, led to nothing. The only
difference between Plato and his scholar lies in the clearness of
intellectual vision which Plato shows when he expressly maintains in
plain words that the universals of exact science are not "in" our
sense-perceptions and therefore to be extracted from them by a process
of abstraction, but are "apart from" or "over" them, and form an ideal
system of interconnected concepts which the experiences of sense merely
"imitate" or make approximation to.
One more point remains to be considered to complete our outline of the
Aristotelian theory of knowledge. The sciences have "principles" which
are discerned to be true by immediate inspection. But what if one man
professes to see the self-evident truth of such an alleged principle,
while another is doubtful of its truth, or even denies it? There can be
no question of silencing the objector by a demonstration, since no
genuine simple principle admits of demonstration. All that can be done,
_e.g._ if a man doubts whether things equal to the same thing are equal
to one another, or whether the law of contradiction is true, is to
examine the consequences of a denial of the axiom and to show that they
include some which are false, or which your antagonist at least
considers false. In this way, by showing the falsity of consequences
which follow from the denial of a given "principle," you indirectly
establish its truth. Now reasoning of this kind differs from "science"
precisely in the point that you take as your major premiss, not what you
regard as true, but the opposite thesis of your antagonist, which you
regard as false. Your object is not to prove a true conclusion but to
show your opponent that _his_ premisses lead to false conclusions. This
is "dialectical" reasoning in Aristotle's sense of the word, _i.e._
reasoning not from your own but from some one else's premisses. Hence
the chief philosophical importance which Aristotle ascribes to
"dialectic" is that it provides a method of defending the undemonstrable
axioms against objections. Dialectic of this kind became highly
important in the mediaeval Aristotelianism of the schoolmen, with whom
it became a regular method, as may be seen _e.g._ in the _Summa_ of St.
Thomas, to begin their consideration of a doctrine by a preliminary
rehearsal of all the arguments they could find or devise against the
conclusion they meant to adopt. Thus the first division of any article
in the _Summa Theologiae_ of Thomas is regularly constituted by
arguments based on the premisses of actual or possible antagonists, and
is strictly dialectical. (To be quite accurate Aristotle should, of
course, have observed that this dialectical method of defending a
principle becomes useless in the case of a logical axiom which is
presupposed by all deduction. For this reason Aristotle falls into
fallacy when he tries to defend the law of contradiction by dialectic.
It is true that if the law be denied, then any and every predicate may
be indifferently ascribed to any subject. But until the law of
contradiction has been admitted, you have no right to regard it as
absurd to ascribe all predicates indiscriminately to all subjects.
Thus, it is only assumed laws which are _not_ ultimate laws of logic
that admit of dialectical justification. If a truth is so ultimate that
it has either to be recognised by direct inspection or not at all, there
can be no arguing at all with one who cannot or will not see it.)
*CHAPTER III*
*FIRST PHILOSOPHY*
First Philosophy is defined by Aristotle as a "science which considers
What Is simply in its character of Being, and the properties which it
has as such." That there is, or ought to be, such a science is urged on
the ground that every "special" science deals only with some restricted
department of what is, and thus considers its subject-matter not
universally in its character of being, or being real, but as determined
by some more special condition. Thus, First Philosophy, the science
which attempts to discover the most ultimate reasons of, or grounds for,
the character of things in general cannot be identified with any of the
"departmental" sciences. The same consideration explains why it is
"First Philosophy" which has to disentangle the "principles" of the
various sciences, and defend them by dialectic against those who impugn
them. It is no part of the duty of a geometer or a physicist to deal
with objections to such universal principles of reasoning as the law of
contradiction. They may safely assume such principles; if they are
attacked, it is not by specifically geometrical or physical
considerations that they can be defended. Even the "principles of the
special sciences" have not to be examined and defended by the special
sciences. They are the starting-points of the sciences which employ
them; these sciences are therefore justified in requiring that they
shall be admitted as a condition of geometrical, or physical, or
biological demonstrations. If they are called in question, the defence
of them is the business of logic.
First Philosophy, then, is the study of "What Is simply as such," the
universal principles of structure without which there could be no
ordered system of knowable objects. But the word "is" has more than one
sense. There are as many modes of being as there are types of
predication. "Substances," men, horses, and the like, have their own
specific mode of being--they are things; qualities, such as green or
sweet, have a different mode of being--they are not things, but
"affections" or "attributes" of things. Actions, again, such as
building, killing, are neither things nor yet "affections" of things;
their mode of being is that they are processes which produce or destroy
things. First Philosophy is concerned with the general character of all
these modes of being, but it is specially concerned with that mode of
being which belongs to _substances_. For this is the most primary of
all modes of being. We had to introduce a reference to it in our
attempt to say what the mode of being of qualities and actions is, and
it would have been the same had our illustrations been drawn from any
other "categories." Hence the central and special problem of First
Philosophy is to analyse the notion of substance and to show the causes
of the existence of substances.