Venn, pp. 112-117 of The Principles of Inductive Logic

[Matt Faunce]

The Principles of Empirical or Inductive Logic, by John Venn, pp. 112-117

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p. 112

CHAPTER V.

THE SUBJECTIVE FOUNDATIONS OF INDUCTION.

We have now examined, with sufficient minuteness and care for our present
purposes, what may be called the objective or material foundations of an
Inductive system of Logic. But, in accordance with the general view already
insisted on, such an examination deals only with one side of our subject.
Logic is neither a purely objective nor a purely subjective science, but
essentially and almost exclusively a science which involves both aspects.
It concerns itself with the operations of the human mind when drawing
inferences about the phenomena of nature. Accordingly we must now enter
into some examination of the second, or mental, side of the enquiry, by
ascertaining the nature of the postulates which have to be demanded from
the regions of Psychology or Metaphysics before a System of Inference can
be constructed.

I. In the first place; it is obvious that the ordinary powers of
observation must be taken for granted. Logic, by universal admission, in
every application we make of it, starts from premises which have been
obtained from observation, directly or remotely. We must therefore include,
amongst our postulates, the existence of these powers of observation. As
however this is in no way peculiar to Logic, but applies in an equal or
even greater degree to many of the special sciences, we need not pause to
examine it as a general postulate.

Where the question does force itself upon our notice, — and indeed, as we
are about to see, raises some very perplexing problems, — is not so much in
respect of the mere assumption of these powers, or in the assignment of
their general character, but rather in the attempted determination of their
boundary line. Where, in fact, are we to suppose that pure Observation

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ends and true Inference begins? In a Science of Inference such a question
as this is a serious one ; and it must be frankly admitted that any doubts
and difficulties which we encounter in answering it constitute a flaw in
the theoretic perfection of the science. Unfortunately however there seems
no way of completely removing such doubts, and all that we can do is to
minimize their consequences.

Any simple example will serve to illustrate the difficulty. Suppose I am on
a walking tour, and a stranger proposes to join our party; I give a glance
at him and say to my friend, 'I can see plainly enough that he will not be
fit for our excursion to-day’. Now though this remark is couched in the
language of mere observation any one uttering it would not need to be
reminded that it is a mixture of observation and inference ; and if he
spoke with less colloquial abbreviation he would intimate the distinction
by expressing himself somewhat as follows, — ‘ I can see that the man is
ill, and therefore I am sure he cannot take a long walk ‘. In common
parlance the present illness is an observation, and the inability to take
the walk is an inference. We might not be consciously thinking of the
distinction at the time, but this is the sort of analysis we should
instantaneously make when attention was directed to the point. Our plain
man would reply, ' you can see for yourself the state he is in. Just look
at him, how ill he is ‘, and so forth.

Now it is a merely elementary step in analysis to point out that the
assumed state of the man, bodily and mental, which is involved in the ‘
illness ‘, is largely a conclusion founded on data. The very expression ‘
symptom ‘, so commonly applied to diseases, is an illustration that the
distinction has been recognized as far as this by all but the rudest and
most unobservant. So far then we have pushed the observation a stage
further back, having resolved it into such elements as the paleness, the
lax or stooping gait, perhaps the quickness of breathing, and so forth,
which are considered to be the symptoms of the disease.

But then begins again the never-ending process of analysis as applied to
these elements themselves. For shortness, take but one of these, the
paleness, where we are purposely confining ourselves to a characteristic
which seems about as simple and elementary as experience can furnish : it
is one of colour pure and simple. But the psychologist has something to say
about

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this. It admits of simple proof that the colour of the man's face, as
perceived by us, varies vastly more according as we see it by daylight or
candlelight, or even according as he stands somewhat more or less in the
shade, than it can possibly vary according to the extremest conditions of
health and sickness whilst the light remains the same. That is, our
subjective estimate of such a simple and apparently ultimate datum as this
of mere colour is in great part an instinctive judgment or inference. What
we really saw is so instantly corrected and allowed for that it actually
drops out of notice, whilst what is effectively retained is something so
different from the former that it must be regarded as very largely
consisting of inference.

Again; suppose that by an effort of reflection, and comparison of the same
shade under varying conditions, we had enabled ourselves to estimate the
colour as it was, that is, as it should be under normal circumstances, —
and the psychologist knows how difficult this would be, — was it really
true that we saw, as we supposed, a surface of that colour? It is highly
unlikely that we did so. What any ordinary glance takes in, when directed
towards a surface, is nothing more than a succession of points which are
supplemented and filled in by something else than sight. At least this is
all that is perceived by the central spot of the retina, which alone is
capable of clear vision. How obstinately our senses refuse to undertake the
drudgery of examining every separate detail in the objects we inspect, even
when we are gazing upon them with some care, is only too well known to
those who have ever worked through a proof sheet as it came from the press.
The almost inevitable impulse is to visualize a few letters and thence to
infer the whole word, and even from a part of a sentence to infer the rest
; and it requires a strong and persistent effort to insist that the eye
shall not thus shirk its work of adequate observation.

Finally; take as minute a fragment of visible area as we choose, so as to
avoid any such spatial filling in as that just indicated : is the
impression really continuous, either in time or space? Confine ourselves,
for the sake of brevity, to the former continuity. It is approximately
certain in the case of sight, and quite certain in the case of sound, that
what seems to us to be

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a continuous elementary impression is really made up of distinct nervous
impulses or shocks. We are not referring here to the fact, familiarly
illustrated by the case of a rapidly revolving point of light, that finite
impressions outlast their producing cause, and so tend, when repeated after
short intervals, to overlap and become continuous. We are here going a
stage further back, and are enquiring into the mode of production of the
most elementary and briefest of such finite impressions themselves; that
is, we are referring to the process by which impulses or shocks which
separately do not emerge into consciousness can yet do so when there is a
sufficient succession of them. The fact itself must of course be taken for
granted here; the only question now before us being whether the distinction
between datum and inference which has been pushed thus far back, is to be
considered capable of receding one stage further still. There are many
psychologists who distinctly claim these non-conscious elements as being as
truly ' mental ‘ as those of which we are conscious ; are we then to admit
that the step from the one to the other is to be regarded as a logical
step, and as being of the nature of inference ?

As we have not yet come to examine into the real nature of inference in the
cases in which its existence is undisputed, it would be impossible to
attempt to decide this question properly here. We will merely indicate in a
few words why such a step as this last is not to be ranked as a logical
one. Briefly, then, Logic is concerned, not necessarily with processes of
which we are conscious at the time, — for many unquestionable inferences
take place spontaneously, and without our being aware at the time that they
are such, — but at any rate with those that can be voluntarily reproduced
when attention is directed to them. This seems the most definite and
convenient point at which to mark the line. In all the successive cases
indicated in the foregoing description, except the last, the process seems
essentially to be of the same character. We had mentally taken a definite
step from one conscious element to another: often no doubt without knowing
that we had done so : but it was always a step which we could, if we
pleased, go over again deliberately. We felt that we could revise or
justify our judgment. But the step which leads us into consciousness is a
very different one from that which only leads us from one point

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to another within its province. The data here were such that no amount
whatever of introspection could possibly set them before us directly: we
can only reach them indirectly by analogy, not start from them
deliberately.

The general conclusion I should draw in respect of our attitude towards any
really ultimate data, is that they can no more be reached than can a first
point or absolute limit in time or space. Everywhere, however far back we
may succeed in pushing our analysis, we find ourselves in the same general
position: — that of having something in hand which implies something beyond
or behind it. The metaphor of the ever-receding horizon which we follow in
vain if we seek to find a terminus there, seems a sound one. We cannot
start from the horizon and work our way steadily from this as a beginning,
up to the point at which we now stand : our path is in the opposite
direction, ever straining towards something which it is impossible for us
actually to attain.

The popular estimate of the claims of Logic is, presumably, that it has a
definite starting point : that if we do not attain ultimate data it is
merely because we have not taken the trouble to go back to them : that
sense or intuition can always furnish them for us. This view is supported
by a stock of common metaphors, which, whether they conceive our path to be
an upward or a downward one, whether, that is, they liken it to a chain
hanging down, or to a building rising up, always suggest a definite
starting point. The links must have some fixed attachment, whence they hang
firmly : the courses of masonry must have a solid foundation, on which they
rest securely ; and so forth. All these metaphors are misleading, unless it
be expressly explained that any such starting point is a merely
conventional one, assumed for convenience. Everywhere, wherever we may
happen to find ourselves, we are in possession of data which are familiar
to us and are justified by experience. These are our starting point, and
not any really primitive data. From thence we proceed, so to say, outwards,
always striving towards absolute origins or elementary data, but without
the slightest hope of ever reaching them.

The attitude of most ordinary persons towards the distinction between
observation and inference is quite in harmony with this view. They do not
indeed deliberately recognize that no

p. 117

ultimate elements can ever be obtained; they do not much trouble themselves
about any such consideration. What they primarily have in view is not the
distinction between observation and inference, but rather that between what
may conveniently be taken for granted and what needs reasons for its
support. The two distinctions are not quite the same thing, but they run
nearly parallel. When, in our example some pages back, the speaker says
that he can see that the stranger is not fit for the expedition, all that
he has in view is that such an opinion will be readily accepted. On this
being questioned he falls back on the statement that he can see the man is
ill, claiming that this at least will pass without question. And so on,
step by step. He is not thinking of anything so technical as ‘pure
observation' and where exactly this may be detected, he is only thinking of
what will be admitted then and there by those to whom he is speaking; and
he is prepared to go as far back, step by step, as may reasonably be
expected until he and they come to some common basis of agreement. But he
would naturally soon become irritated with any one who kept up the
analytical cross-examination too long, on the ground that it was quibbling
about points which no rational person could doubt.

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Matt