Psychology as a scientific discipline is only two generations old, the first laboratory having been founded in 1879. Educational psychology is considerably younger, for it was only natural that the early workers in the new field should be completely engrossed in devising investigational methods and in laying the broad outlines of the science as a whole with little regard to its practical values. When later the importance of psychology for education began to be recognized, treatises were written which explained the applications of psychological laws to the teaching process. For some time educational psychology was thus nourished almost entirely from crumbs that fell from the table of the so-called "pure" psychologist, with the result that the latter was often inclined to regard it with a certain amount of contempt. When later the problems of educational psychology began to be investigated on their own account, it was found that the line between pure and applied science is more imaginary than real and that science itself is largely dependent for its growth on the motivation that has its source in practical issues.

To-day educational psychology is no longer applied psychology in the old sense of the term. It is one of the most important aspects of the general science, just as psycho-pathology is, and just as animal behavior is. Its methods, devised for such specific purposes as investigating individual differences, mental development, and the facts of learning, have profoundly influenced psychological methods in general. Its results, likewise, have been incorporated into the science and are helping to shape psychological theory. The educational psychologist is merely a psychologist who prefers to work with problems that happen to have a bearing upon education; actually his personal interest may have less to do with education, as such, than with the eternal verities of human nature.

If we define education as the making of changes in human nature, then nothing which concerns human nature can be entirely alien to it. One might go further and say that nothing which concerns the behavior of any biological organism can be entirely alien to it, for there are important principles that apply to all living things. Nevertheless, there are certain aspects of biological science, and more particularly of psychological science, that concern education much more than others, and it is these only that can be touched upon in this cursory review. The present discussion will therefore be limited to the following topics: (1) instinctive tendencies, (2) individual differences and their causes, (3) psychometric methods, (4) mental development, and (5) the psychology of learning.

Instinctive Tendencies. If the purpose of education is to make human behavior different from what it would be without education, it is necessary to take account of what original nature has given. This must be done in two directions : (1) we must consider instinctive tendencies, and (2) we must take account of capacity to modify original nature - that is, of intelligence or ability to learn. In both of these types of endowment there may exist individual differences over and above the traits which characterize human beings as such, and in the field of intelligence the differences are especially important. We shall consider first the problem of human instincts, one of the most controversial issues in present-day psychology.

The point of view made popular by William James, that man has many well-defined instincts - more than other animals, rather than fewer - was generally accepted by educational psychologists for a quarter of a century. The long list of human instincts compiled by James was followed in 1906 by the similar though somewhat briefer list of McDougall. McDougall's presentation of the instinct problem, which for a decade or more greatly influenced thinking in educational as well as in social psychology, had much in common with that of James. Both regarded instincts as primary determiners of a great fraction of human behavior, as psychobiological forces which give direction to all our striving. According to McDougall the essential nature of an instinct is not to be sought in the exact mode of response to a particular stimulus, but in its goal-seeking and purposive character which may cause it to find expression now in one type of response and now in another. Then in 1913 followed Thorndike's treatment of the subject, somewhat more in the vein of James than of McDougall, but resembling both in the extended list of instincts posited. For Thorn-dike, however, an instinct is an innate bond between a specific stimulus and a specific response, and not the generalized psychophysical disposition assumed by McDougall. Instincts in McDougall's sense he regards as pseudo-entities that have no existence in reality. The important thing to know is the particular response that follows or tends to follow a particular stimulus. Thorn-dike's psychology of instinct, like his psychology of learning and of intelligence, is a bond psychology. It is thus essentially a revamping into biological terminology of the older association psychology given vogue by Locke, Hume, the two Mills, and Herbart.

In recent years there has been a strong, not to say violent, reaction against the older doctrines of instinct, especially against that of McDougall. This reaction has taken the form of gross reduction in the number of instincts posited, and has even gone to the extreme of denying that any instincts, either human or animal, exist at all. The denial of instincts to animals need not, of course, be taken seriously. To believe that all the myriad behavior patterns of animals are learned rather than innate is obviously absurd. The arguments against the existence of human instincts, however, are more plausible. If we follow the behaviorists in defining instinct as a specific response to a given stimulus, then it must be admitted that, with the exception of a small number of reflex responses in the young infant, there are no human instincts. Apart from these, the child's behavior is soon modified to such an extent by learning that few well-defined, persistent, and universal pattern reactions are discoverable.