r worse than before. Thus you discover which set of conditions
is more favorable for memorizing, and thence can infer something of
the way in which memorizing is accomplished. In the whole experiment
you need not have called on your subject for any introspections; and
this is a type of many experiments in which the subject accomplishes a
certain task under known conditions, and his success is objectively
observed and measured.

There is another type of objective psychological observation, directed
not towards the success with which a task is accomplished, but towards
the changes in breathing, heart beat, stomach movements, brain
circulation, or involuntary movements of the hands, eyes, etc., which
occur during the course of various mental processes, as in reading, in
emotion, in dreaming or waking from sleep.

Now it is not true as a matter of history that either of these types
of objective observation was introduced into psychology by those who
call themselves behaviorists. Not at all; experiments of both sorts
have been common in psychology since it began to be an experimental
science. The first type, the success-measuring experiment, has been
much more used than introspection all along. What the behaviorists
have accomplished is the definitive overthrow of the doctrine, once
strongly insisted on by the "consciousness psychologists", that
introspection is the only real method of observation in psychology;
and this is no mean achievement. But we should be going too far if we
followed the behaviorists to the extent of seeking to exclude
introspection altogether, and on principle. There is no sense in such
negative principles. Let us accumulate psychological facts by any
method that will give the facts.

{14}

General Laws of Psychological Investigation.

Either introspective or objective observation can be employed in the
_experimental attack_ on a problem, which consists, as just
illustrated in the case of memory, in controlling the conditions under
which a mental performance occurs, varying the conditions
systematically, and noting the resulting change in the subject's
mental process or its outcome. Psychologists are inclined to regard
this as the best line of attack, whenever the mental activity to be
studied can be effectively subjected to control. Unfortunately,
emotion and reasoning are not easily brought under control, and for
this reason psychology has made slower progress in understanding them
than it ha