INFERENCE AS A HABIT
In this chapter, we are concerned with inference as it can be observed
when practised by some one else. Inference is supposed to be a mark of
intelligence and to show the superiority of men to machines. At the
same time, the treatment of inference in traditional logic is so stupid
as to throw doubt on this claim, and syllogistic inference, which was
taken as the type from Aristotle to Bacon (exclusive), is just the sort
of thing that a calculating machine could do better than a professor.
In syllogistic inference, you are supposed to know already that all
men are mortal and that Socrates is a man; hence you deduce, what you
never suspected before, that Socrates is mortal. This form of inference
does actually occur, though very rarely. The only instance I have ever
heard of was supplied by Dr. F. C. S. Schiller. He once produced a
comic number of the philosophical periodical _Mind_, and sent copies to
various philosophers, among others to a certain German, who was much
puzzled by the advertisements. But at last he argued: “Everything in
this book is a joke, therefore the advertisements are jokes”. I have
never come across any other case of new knowledge obtained by means of
a syllogism. It must be admitted that, for a method which dominated
logic for two thousand years, this contribution to the world’s stock of
information cannot be considered very weighty.
The inferences that we actually make in daily life differ from those
of syllogistic logic in two respects, namely, that they are important
and precarious, instead of being trivial and safe. The syllogism may be
regarded as a monument to academic timidity: if an inference might be
wrong, it was dangerous to draw it. So the mediæval monks, in their
thinking as in their lives, sought safety at the expense of fertility.
With the Renaissance, a more adventurous spirit came into the world,
but at first in philosophy, it only took the form of following Greeks
other than Aristotle, and more especially Plato. It is only with Bacon
and Galileo that the inductive method arrived at due recognition:
with Bacon as a programme which was largely faulty, but with Galileo
as something which actually led to brilliant results, namely, the
foundation of modern mathematical physics. Unfortunately, when the
pedants got hold of induction, they set to work to make it as tame and
scholastic as deduction had been. They searched for a way of making
it _always_ lead to true results, and in so doing robbed it of its
adventurous character. Hume turned upon them with sceptical arguments,
proving quite conclusively that if an induction is worth making it may
be wrong. Thereupon Kant deluged the philosophic world with muddle and
mystery, from which it is only now beginning to emerge. Kant has the
reputation of being the greatest of modern philosophers, but to my mind
he was a mere misfortune.
Induction, as it appears in the text-books, consists, roughly
speaking, in the inference that, because A and B have been found often
together and never apart, therefore they are probably always together,
and either may be taken as a sign of the other. I do not wish, at
this stage, to examine the logical justification of this form of
argumentation; for the present, I am considering it as a _practice_,
which we can observe in the habits of men and animals.
As a practice, induction is nothing but our old friend, the law of
conditioned reflexes or of association. A child touches a knob that
gives him an electric shock; after that, he avoids touching the knob.
If he is old enough to speak he may state that the knob hurts when it
is touched; he has made an induction based on a single instance. But
the induction will exist as a bodily habit even if he is too young
to speak, and it occurs equally among animals, provided they are not
too low in the scale. The theories of induction in logic are what
Freudians call a “rationalisation”; that is to say, they consist of
reasons invented afterwards to prove that what we have been doing is
sensible. It does not follow that they are bad reasons; in view of the
fact that we and our ancestors have managed to exist since the origin
of life, our behaviour and theirs must have been fairly sensible, even
if we and they were unable to prove that it was. This, however, is not
the point that concerns us at present. What concerns us at present is
the fact that verbal induction is a late development of induction in
behaviour, which is nothing more or less than the principle of “learned
reactions”.
This principle, as the reader will remember, states that, if a
certain event calls out a certain response, and if another event is
experienced just before it, or at the same moment, in time that other
event will tend to call out the response which, originally, only
the first event would call out. This applies both to muscles and to
glands; it is because it applies to glands that words are capable of
causing emotions. Moreover, we cannot set limits to the length of the
chain of associations that may be established. If you hold an infant’s
limbs, you call out a rage reaction; this appears to be an “unlearned
reaction”. If you, and no one else, repeatedly hold an infant’s limbs,
the mere sight of you will call out a rage reaction after a time.
When the infant learns to talk your name may have the same effect.
If, later, he learns that you are an optician, he may come to hate
all opticians; this may lead him to hate Spinoza because he made
spectacles, and thence he may come to hate metaphysicians and Jews.
For doing so he will no doubt have the most admirable reasons, which
will seem to him to be his real ones; he will never suspect the process
of conditioning by which he has in fact arrived at his enthusiasm for
the Ku Klux Klan. This is an example of conditioning in the emotional
sphere; but it is rather in the muscular sphere that we must seek the
origin of the practice of induction.
Domestic animals which are habitually fed by a certain person will run
towards that person as soon as they see him. We say that they expect
food, and in fact their behaviour is very like what it would be if
they saw food. But really we have only an example of “conditioning”:
they have often seen first the farmer and then the food, so that in
time they react to the farmer as they originally reacted to the food.
Infants soon learn to react to the sight of the bottle, although at
first they only react to the touch of it. When they can speak, the same
law makes them say “dinner” when they hear the dinner-bell. It is quite
unnecessary to suppose that they first think “that bell means dinner”,
and then say “dinner”. The sight of dinner (by previous “learned
reaction”) causes the word “dinner”: the bell frequently precedes the
sight of dinner; therefore in time the bell produces the word “dinner”.
It is only subsequent reflection, probably at a much later age, that
makes the child say “I knew dinner was ready because I heard the bell”.
Long before he can say this, he is acting as if he knew it. And there
is no good reason for denying that he knows it, when he acts as if he
did. If knowledge is to be displayed by behaviour, there is no reason
to confine ourselves to _verbal_ behaviour as the sole kind by which
knowledge can manifest itself.
The situation, stated abstractly, is as follows. Originally, stimulus
A produced reaction C; now stimulus B produces it, as a result of
association. Thus B has become a “sign” of A, in the sense that it
causes the behaviour appropriate to A. All sorts of things may be signs
of other things, but with human beings words are the supreme example of
signs. All signs depend upon some practical induction. Whenever we read
or hear a statement, its effect upon us depends upon induction in this
sense, since the words are signs of what they mean, in the sense that
we react to them, in certain respects, as we should to what they stand
for. If some one says to you “your house is on fire”, the effect upon
you is practically the same as if you saw the conflagration. You may,
of course, be the victim of a hoax, and in that case your behaviour
will not be such as achieves any purpose you have in view. This risk
of error exists always, since the fact that two things have occurred
together in the past cannot prove conclusively that they will occur
together in the future.
Scientific induction is an attempt to regularise the above process,
which we may call “physiological induction”. It is obvious that, as
practised by animals, infants, and savages, physiological induction is
a frequent source of error. There is Dr. Watson’s infant who induced,
from two examples, that whenever he saw a certain rat there would be
a loud noise. There is Edmund Burke, who induced from one example
(Cromwell) that revolutions lead to military tyrannies. There are
savages who argue, from one bad season, that the arrival of a white
man causes bad crops. The inhabitants of Siena, in 1348, thought
that the Black Death was a punishment for their pride in starting to
build too large a cathedral. Of such examples there is no end. It is
very necessary, therefore, if possible, to find some method by which
induction can be practised so as to lead, in general, to correct
results. But this is a problem of scientific method, with which we will
not yet concern ourselves.
What does concern us at present is the fact that all inference, of
the sort that really occurs, is a development of this one principle
of conditioning. In practice, inference is of two kinds, one typified
by induction, the other by mathematical reasoning. The former is by
far the more important, since, as we have seen, it covers all use of
signs and all empirical generalisations as well as the habits of which
they are the verbal expression. I know that, from the traditional
standpoint, it seems absurd to talk of inference in most cases of this
sort. For example, you find it stated in the paper that such and such a
horse has won the Derby. According to my own use of words, you practise
an induction when you arrive thence at the belief that that horse has
won. The stimulus consists of certain black marks on white paper--or
perhaps on pink paper. This stimulus is only connected with horses
and the Derby by association, yet your reaction is one appropriate
to the Derby. Traditionally, there was only inference where there
was a “mental process”, which, after dwelling upon the “premisses”,
was led to assert the “conclusion” by means of insight into their
logical connection. I am not saying that the process which such words
as the above are intended to describe never takes place; it certainly
does. What I am saying is that, genetically and causally, there is no
important difference between the most elaborate induction and the most
elementary “learned reaction”. The one is merely a developed form of
the other, not something radically different. And our determination to
believe in the results of inductions, even if, as logicians, we see
no reason to do so, is really due to the potency of the principle of
association; it is an example--perhaps the most important example--of
what Dr. Santayana calls “animal faith”.
The question of mathematical reasoning is more difficult. I think we
may lay it down that, in mathematics, the conclusion always asserts
merely the whole or part of the premisses, though usually in new
language. The difficulty of mathematics consists in seeing that
this is so in particular cases. In practice, the mathematician has
a set of rules according to which his symbols can be manipulated,
and he acquires technical skill in working according to the rules
in the same sort of way as a billiard-player does. But there is a
difference between mathematics and billiards: the rules of billiards
are arbitrary, whereas in mathematics some at least are in some sense
“true”. A man cannot be said to understand mathematics unless he
has “seen” that these rules are right. Now what does this consist
of? I think it is only a more complicated example of the process of
understanding that “Napoleon” and “Bonaparte” refer to the same person.
To explain this, however, we must revert to what was said, in the
chapter on “Language”, about the understanding of form.
Human beings possess the power of reacting to form. No doubt some of
the higher animals also possess it, though to nothing like the same
extent as men do; and all animals, except a few of the most intelligent
species, appear to be nearly devoid of it. Among human beings, it
differs greatly from one individual to another, and increases, as a
rule, up to adolescence. I should take it as what chiefly characterises
“intellect”. But let us see, first, in what the power consists.
When a child is being taught to read, he learns to recognise a given
letter, say H, whether it is large or small, black or white or red.
However it may vary in these respects his reaction is the same: he
says “H”. That is to say, the essential feature in the stimulus is its
_form_. When my boy, at the age of just under three, was about to eat a
three-cornered piece of bread and butter, I told him it was a triangle.
(His slices were generally rectangular.) Next day, unprompted, he
pointed to triangular bits in the pavement of the Albert Memorial, and
called them “triangles”. Thus the form of the bread and butter, as
opposed to its edibility, its softness, its colour, etc., was what had
impressed him. This sort of thing constitutes the most elementary kind
of reaction to form.
Now “matter” and “form” can be placed, as in the Aristotelian
philosophy, in a hierarchy. From a triangle we can advance to a
polygon, thence to a figure, thence to a manifold of points. Then we
can go on and turn “point” into a formal concept, meaning “something
that has relations which resemble spatial relations in certain formal
respects”. Each of these is a step away from “matter” and further into
the region of “form”. At each stage the difficulty increases. The
difficulty consists in having a uniform reaction (other than boredom)
to a stimulus of this kind. When we “understand” a mathematical
expression, that means that we can react to it in an appropriate
manner, in fact, that it has “meaning” for us. This is also what we
mean by “understanding” the word “cat”. But it is easier to understand
the word “cat”, because the resemblances between different cats are
of a sort which causes even animals to have a uniform reaction to all
cats. When we come to algebra, and have to operate with _x_ and _y_,
there is a natural desire to know what _x_ and _y_ really are. That,
at least, was my feeling: I always thought the teacher knew what they
really were, but would not tell me. To “understand” even the simplest
formula in algebra, say (x + y)² = x² + 2xy + y², is to be able to
react to two sets of symbols in virtue of the form which they express,
and to perceive that the form is the same in both cases. This is a
very elaborate business, and it is no wonder that boys and girls find
algebra a bugbear. But there is no novelty _in principle_ after the
first elementary perceptions of form. And perception of form consists
merely in reacting alike to two stimuli which are alike in form but
very different in other respects. For, when we can do that, we can say,
on the appropriate occasion, “that is a triangle”; and this is enough
to satisfy the examiner that we know what a triangle is, unless he is
so old-fashioned as to expect us to reproduce the verbal definition,
which is of course a far easier matter, in which, with patience, we
might teach even a parrot to succeed.
The meanings of complex mathematical symbols are always fixed by rules
in relation to the meaning of simpler symbols; thus their meanings are
analogous to those of sentences, not to those of single words. What was
said earlier about the understanding of sentences applies, therefore,
to any group of symbols which, in mathematics, will be declared to have
the same meaning as another group, or part of that meaning.
We may sum up this discussion by saying that mathematical inference
consists in attaching the same reactions to two different groups of
signs, whose meanings are fixed by convention in relation to their
constituent parts, whereas induction consists, first, in taking
something as a sign of something else, and later, when we have learned
to take A as a sign of B, in taking A as also a sign of C. Thus the
usual cases of induction and deduction are distinguished by the fact
that, in the former, the inference consists in taking one sign as
a sign of two different things, while in the latter the inference
consists in taking two different signs as signs of the same thing.
This statement is a little too antithetical to be taken as an exact
expression of the whole truth in the matter. What is true, however, is
that both kinds of inferences are concerned with the relation of a sign
to what it signifies, and therefore come within the scope of the law of
association.