But to say, as used to be said, that psychology is purely an introspective science, making use of no other sort of observation, is absurd in the face of the facts.{12}

We have animal psychology, where the observation is exclusively objective. In objective observation, the observer watches something else, and not himself. In animal psychology, the psychologist, as observer, watches the animal.

The same is true of child psychology, at least for the first years of childhood. You could not depend on the introspections of a baby, but you can learn much by watching his behavior. Abnormal persons, also, are not often reliable introspectionists, and the study of abnormal psychology is mostly carried on by objective methods.

Now how is it with the normal adult human being, the standard subject for psychology? Does he make all the observations on himself or may he be objectively observed by the psychologist? The latter, certainly. In fact, nearly all tests, such as those used in studying differential psychology, are objective. That is to say that the person tested is given a task to perform, and his performance is observed in one way or another by the examiner. The examiner may observe the time occupied by the subject to complete the task, or the quantity accomplished in a fixed time; or he may measure the correctness and excellence of the work done, or the difficulty of the task assigned. One test uses one of these measures, and another uses another; but they are all objective measures, not depending at all on the introspection of the subject.

What is true of tests in differential psychology is true of the majority of experiments in general psychology: the performer is one person, the observer another, and the observation is objective in character. Suppose, for example, you are investigating a memory problem; your method may be to set your subject a lesson to memorize under certain defined conditions, and see how quickly and well he learns it; then you give him another, equally difficult lesson to be learned under altered conditions, and observe whether he {13} does better or 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}