only in so far as they constitute
response. Otherwise his study is not a study of behavior, but a study of
movements. But when does a movement constitute a response? Do we label
as stimulus the spoken word which results in overt action a week later,
or the visual perception which sets a complicated and long-drawn-out
problem, for no other reason than that it appears somewhere as an
antecedent in the causal chain of events? If so, there is no obvious
reason why the event which occurred just before or immediately after the
_soi-disant_ stimulus should not be regarded as the true stimulus.
Unless a satisfactory reason is forthcoming, it would seem better to
substitute cause and effect for stimulus and response and to drop the
term behavior from our vocabulary. Psychology then becomes a study of
certain causal relationships, but is still without a principle for the
selection of those causal events which are supposed to constitute its
peculiar subject-matter.

Even if we manage to become reconciled to this situation, however, our
troubles are not yet at an end. There still remains the difficulty in
certain cases of showing that the event which is selected as stimulus or
cause bears any significant relationship to the event which figures in
our scheme as the response. The stimulus is supposed to have a causal
connection with the response, but how are we to know that this is the
fact? How are we to know that the engineer who solves a problem for me
at my request might not have done so anyway? No behaviorist can possibly
show that the air waves set in motion by my vocalization were an
indispensable stimulus. We doubtless believe that the spoken word was in
fact the spark which lit the fuse and finally exploded the mine, but
this belief involves a complication of causes which it is wholly beyond
our power to control or to verify.

It is true, of course, that we are able, as a matter of fact, to
correlate stimulus and response. I know that it was the spoken word
which caused the commission to be executed, for the expert reminds me of
the fact and presents a bill. But neither of us makes any pretense that
his belief is derived from a scrutiny of the causal sequence. Memory
furnishes us with a shortcut to the result. While our present acts are
doubtless connected with the past through causation, we do not regard
them as simply the effects of antecedent causes. They are rather
responses to present stimuli. The expert presents his b