action before us
for explanation, we have to ask what the stimulus is that arouses the
individual to activity, and how he responds. Stimulus-response
psychology is solid, and practical as well; for if it can establish
the laws of reaction, so as to predict what response will be made to a
given stimulus, and what stimulus can be depended on to arouse a
desired response, it furnishes the "knowledge that is power". Perhaps
no more suitable motto could be inscribed over the door of a
psychological laboratory than these two words, "Stimulus-Response."

Such a motto would not frighten away the modern introspectionists, for
they, no less than the behaviorists, could find a congenial home in a
stimulus-response laboratory. They would begin by studying sensations,
and, advancing to more complex responses, would observe the conscious
processes entering into the response.

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But, however useful the reaction may be as affording a sound basis for
psychological study, we must not allow it to blind our eyes to any of
the real facts of mental life; and, at first thought, it seems as if
_motives, interests_ and _purposes_ did not fit into the
stimulus-response program. Many hard-headed psychologists have fought
shy of such matters, and some have flatly denied them any place in
scientific psychology. But let us see.

_S ---> R_

[Illustration: Fig. 20.--The symbol of stimulus-response psychology.
_S_ means the stimulus, and _R_ the response. The line between is the
connection from stimulus to response.]

Suppose we are looking out on a city street during the noon hour. We
see numbers of people who--lunch over, nothing to do till one
o'clock!--are standing or walking about, looking at anything that
chances to catch their eye, waving their hands to friends across the
street, whistling to a stray dog that comes past, or congregating
about an automobile that has broken down in the crowded thoroughfare.
These people are responding to stimuli, obviously enough, and there is
no difficulty in fitting their behavior into the stimulus-response
scheme.

But here comes some one who pays little attention to the sights and
sounds of the street, simply keeping his eyes open enough to avoid
colliding with any one else. He seems in a hurry, and we say of him,
"He must have business on hand; he has to keep an appointment or catch
a train". He is not simply responding to the stimuli that come to him,
but has some purpose of his own tha