Strictly speaking, comparative psychology ought to involve the use of a comparative method, in which similar studies are carried out on animals of different species, and the results interpreted in terms of their different phylogenetic or ecological backgrounds. Throughout the long history of comparative psychology, repeated attempts have been made to enforce this more disciplined approach, especially since the rise of ethology in the mid twentieth century, and behavioral ecology in the 1970s gave a more solid base of knowledge against which a true comparative psychology could develop. However, the broader use of the term "comparative psychology" is enshrined in the names of learned societies and academic journals, not to mention in the minds of psychologists of other specialisms, so it is never like to disappear completely.

A persistent question with which comparative psychologists have been faced is the relative intelligence of different species of animal. Much effort has gone into explaining that this may not be a good question, but it will not go away. Indeed, some early attempts at a genuinely comparative psychology involved evaluating how well animals of different species could learn different tasks. However these attempts foundered; in retrospect it can be seen that they were not sufficiently sophisticated, either their analysis of the demands of different tasks, or in their choice of species to compare. More recent comparative work has been more successful, partly because it has drawn upon studies in ethology and behavioral ecology to make informed choices of species and tasks to compare.