CY that a
knowledge-response must have. It is clear from many instances that
accuracy, in other cases, may be purely mechanical. The most complete
form of accuracy consists in giving correct answers to questions, an
achievement in which calculating machines far surpass human beings. In
asking a question of a calculating machine, you must use its language:
you must not address it in English, any more than you would address
an Englishman in Chinese. But if you address it in the language it
understands, it will tell you what is 34521 times 19987, without a
moment's hesitation or a hint of inaccuracy. We do not say the machine
KNOWS the answer, because it has no purpose of its own in giving the
answer: it does not wish to impress you with its cleverness, or feel
proud of being such a good machine. But as far as mere accuracy goes,
the machine leaves nothing to be desired.

Accuracy of response is a perfectly clear notion in the case of answers
to questions, but in other cases it is much more obscure. We may say
generally that an object whether animate or inanimate, is "sensitive" to
a certain feature of the environment if it behaves differently according
to the presence or absence of that feature. Thus iron is sensitive to
anything magnetic. But sensitiveness does not constitute knowledge, and
knowledge of a fact which is not sensible is not sensitiveness to
that fact, as we have seen in distinguishing the fact known from the
stimulus. As soon as we pass beyond the simple case of question and
answer, the definition of knowledge by means of behaviour demands the
consideration of purpose. A carrier pigeon flies home, and so we say
it "knows" the way. But if it merely flew to some place at random, we
should not say that it "knew" the way to that place, any more than a
stone rolling down hill knows the way to the valley.

On the features which distinguish knowledge from accuracy of response in
general, not much can be said from a behaviourist point of view without
referring to purpose. But the necessity of SOMETHING besides accuracy of
response may be brought out by the following consideration: Suppose
two persons, of whom one believed whatever the other disbelieved,
and disbelieved whatever the other believed. So far as accuracy and
sensitiveness of response alone are concerned, there would be nothing to
choose between these two persons. A thermometer which went down for warm
weather and up for cold might be just as accurate