The third method by which it has been attempted to attack the problems of psychology is that which I have called the comparative. Its characteristic note is a distrust of that attitude towards phenomena which I have called the human point of view. Man’s description and interpretation of his own mental experience being so liable to distortion by prejudice, by self-esteem, by his views as to his own nature and powers, as well as so incomplete by reason of his incapacity to reach by ordinary introspection the deeper strata of his mind, it becomes necessary to make action as far as possible the subject of observation rather than speech, and to regard it as a touchstone of motive more important than the actor’s own views. The principle {92} may be exemplified in a simple and concrete form. If a given piece of human behaviour bears the closest resemblance to behaviour which is characteristic of the ape, the sheep, or the wolf, the biologist in attempting to arrive at the actual cause will ascribe an importance to this resemblance at least no less than that he will give to any explanation of the action as rational and deliberate which may be furnished by the actor or by his own intelligence. A second principle of the method will be by a study of the whole range of animal life, and especially of forms whose conduct presents obvious resemblances to that of man, to discover what instinctive impulses may be expected to operate in him. A third principle will be to search for criteria, whereby instinctive impulses or their derivatives arising in the mind can be distinguished from rational motives, or at any rate motives in which the instinctive factor is minimal. Thus will be furnished for the method the objective standard for the judgment of mental observations which is the one indispensable requirement in all psychological inquiries. When it is known what types of instinctive mechanisms are to be expected, and under what aspects they will appear in the mind, it is possible to press inquiry into many of the obscurer regions of human behaviour and thought, and to arrive at conclusions which, while they are in harmony with the general body of biological science, have the additional value of being immediately useful in the conduct of affairs.