So far as I can see, the pronounced tendency to regard the perceived
object as itself the object of a peculiar kind of knowledge instead of
as a term in knowledge of the practical kind has two causes. One is
the confirmed habit of neglecting the wide scope and import of
practical judgments. This leads to overlooking the responsive act as
the other term indicated by the perception, and to taking the
perceived object as the whole of the situation just by itself. The
other cause is the fact that because perceived objects are constantly
employed as evidence of what is to be done--or how to do
something--they themselves become the objects of prolonged and
careful scrutiny. We pass naturally and inevitably from recognition to
_observation_. Inference will usually take care of itself if the datum
is properly determined. At the present day, a skilled physician will
have little difficulty in inferring typhoid instead of malaria from
certain symptoms provided he can make certain observations--that is,
secure certain data from which to infer. The labor of intelligence is
thus transferred from inference to the determination of data, the data
being determined, however, in the interests of inference and as parts
of an inference.
At this point, a significant complication enters in. The ordinary
assumption in the discussion of the relation of perceived objects to
knowledge is that "the" object--the real object--of knowledge in
perception is the thing which _caused_ the qualities which are given.
It is assumed, that is, that the other term of a proposition in which
a sense datum is one term must be the thing which produced it. Since
this producing object does not for the most part appear in ordinary
sense perception, we have on our hands perception as an
epistemological problem--the relation of an appearance to some reality
which it, somehow, conceals rather than indicates. Hence also the
difficulties of "reconciling" scientific knowledge in physics where
these causes are the terms of the propositions with "empirical" or
sense perception knowledge where they do not even appear. Here is
where the primary advantage of recognizing that ordinary sense
perceptions are forms of practical judgment comes in. In practical
judgments, the other term is as open and aboveboard as is the sensory
quality: it is the thing to be done, the response to be selected. To
borrow an illustration of Professor Woodbridge's: A certain sound
indicates to the mother that her baby needs attention. If she turns
out to be in error, it is not because sound ought to mean so many
vibrations of the air, and as matter of fact doesn't even suggest air
vibrations, but because there is wrong inference as to the act to be
performed.
I imagine that if error never occurred in inferences of this practical
sort the human race would have gone on quite contented with them.
However that may be, errors _do_ occur and the endeavor to control
inference as to consequences (so as to reduce their likelihood of
error) leads to propositions where the knowledge-object of the
perceived thing is not something to be done, but the cause which
produced it. The mother finds her baby peacefully sleeping and says
the baby didn't _make_ the noise. She investigates and decides a
swinging door _made_ it. Instead of inferring a consequence, she
infers a cause. If she had identified the noise in the first place,
she would have concluded that the hinges needed oiling.
Now where does the argument stand? The proper control of inference in
specific cases is found (_a_) to lie in the proper identification of
the datum. If the perception is of a certain kind, the inference
takes place as a matter of course; or else inference can be suspended
until more adequate data are found, and thus error is avoided even if
truth be not found. Furthermore (_b_) it is discovered that the most
effective way of identifying datum (and securing adequate data) is by
inference to its cause. The mother stops short with the baby and the
door as causes. But the same motives which made her transfer her
inference from consequences to conditions are the motives which lead
others to inferring from sounds to vibrations of air. Hence our
scientific propositions about sensory data. They are not, as such,
about things to do, but about things which have been done, have
happened--"facts." But they have reference, nevertheless, to
inferences regarding consequences to be effected. They are the means
of securing data which will prevent errors which would otherwise
occur, and which facilitate an entirely new crop of inferences as to
possibilities--means and ends--of action. That scientific men should
be conscious of this reference or even interested in it is not at all
necessary, for I am talking about the logic of propositions, not about
biography nor psychology. If I reverted to psychology, it would be to
point out that there is no reason in the world why the practical
activity of some men should not be predominantly directed into the
pursuits connected with discovery. The extent in which they actually
are so directed depends upon social conditions.