Now in this classification, notwithstanding that it is needful to quote at least ten distinct terms which are either now in use among psychologists or have been used by classical English writers upon these topics, we may observe that there are really but three separate classes to be distinguished. Moreover, it will be noticed that, for the sake of definition, I restrict the first three terms to denote memories of particular sensuous perceptions—refusing, therefore, to apply them to those blended memories of many sensuous perceptions which enable animals and infants (as well as ourselves) to form compound ideas of kind or class without the aid of language. Again, the first division of this threefold classification has to do only with what are termed percepts, while the last has to do only with what are termed concepts. Now there does not exist any equivalent word to meet the middle division. And this fact in itself shows most forcibly the state of ambiguous confusion into which the classification of ideas has been wrought. Psychologists of both the schools that we are considering—namely, those who maintain and those who deny that there is any difference of kind between the ideation of men and animals—are equally forced to allow that there is a great difference between what I have called a simple idea and what I have called a compound idea. In other words, it is a matter of obvious fact that the only distinction between ideas is _not_ that between the memory of a particular percept and the formation of a named concept; for between these two classes of ideas there obviously lies another class, in virtue of which even animals and infants are able to distinguish individual objects as belonging to a sort or kind. Yet this large and important territory of ideation, lying between the other two, is, so to speak, unnamed ground. Even the words “compound idea,” “complex idea,” and “mixed idea,” are by me restricted to it without the sanction of previous usage; for, as above remarked, so completely has the existence of this intermediate land been ignored, that we have no word at all which is applicable to it in the same way that Percept and Concept are applicable to the lands on either side of it. The consequence is that psychologists of the one school invade this intermediate province of ideation with terms that are applicable only to the lower province, while psychologists of the other school invade it with terms which are applicable only to the higher: the one matter upon which they all appear to agree being that of ignoring the wide area which this intermediate territory covers—and, consequently, also ignoring the great distance by which the territories on either side of it are separated.