The process by which animals learn to distinguish what they have previously confused, or to identify for practical purposes what they have previously treated as different is rather one of tentative groping than of express comparison. "Even in a blindly tentative process, the failure of the wrong alternatives will gradually decrease the chance of their renewal."* Under circumstances in which it has been previously deceived, an animal will become more cautious and attentive, thus affording opportunity for the presentation of differences, definite or indefinite, which have previously escaped its notice. In so far as this takes place, its behaviour will become gradually altered in the two cases, respectively. The unsuccessful action will become fainter and less persistent until it disappears, and the converse will hold of the successful action. All this may take place without express comparison of two objects, groups of circumstances, or lines of conduct, having for its aim the marking off of points of difference from points of agreement or of points of agreement from points of difference. Thus a dog, in first learning the trick of opening a gate by a latch, will, to begin with, scratch all over the gate. In doing so, he accidentally hits upon the right movement. On the next occasion, there may be almost as much preliminary groping as before. It is only gradually that the unsuccessful activity is discontinued, and the successful method adopted unhesitatingly from the outset. This is simply a case of the general principle that activity, obstructed in one direction, tends to divert itself into other channels. When animals learn in this way, they are not aware why one course is right and another wrong. The right course is simply forced upon their attention by the circumstances of the case.

* Analytic Psychology, vol. ii.

Comparison in all but a most rudimentary form is an ideational activity. Even when the objects compared are both present to the senses, each is scrutinised in turn. For anything more than a vague awareness of resemblance or difference, it is necessary to keep before the mind the ideal representation of the one object in the very act of examining the other. Only in this way can each detail and characteristic in turn be selected for comparison, so as to distinguish the points of difference from the points of agreement. Hence we may attribute the absence of comparison in animals in all but its most vague and rudimentary form, to the absence or extremely imperfect development of ideational activity in general.

When the process of deliberate comparison plays an important part in the mental life, it involves a corresponding development in conceptual thinking, in the distinction of the general or universal from the particular. To compare is always to compare in some special respect. Some theoretical or practical end is to be subserved by the comparison. The difference or agreement to be discovered is not any difference or agreement, but one which has significance for the guidance of conduct or for the solution of a theoretical difficulty. Thus comparison takes place only in regard to the characteristics which happen to be interesting at the moment, other characteristics being disregarded or set aside as unimportant. Objects in other ways most diverse may yet in a certain respect be compared and found more or less similar, and objects in other ways most similar may be compared in a certain respect and found more or less unlike. Hence, as the process advances it becomes possible to group objects according to the degrees of their difference or resemblance in this or that respect without taking into account their other attributes. We may arrange musical tones according to the degree of their loudness, disregarding their pitch, or according to their pitch disregarding their loudness. In the scale of loudness, sounds most different in pitch might occupy the same position, and sounds of the same pitch widely different positions. A shrill note and a low one may be of equal loudness, and sounds of the same pitch may be of different loudness.

It is evident that in this way what we have called the conceptual analysis of the concrete details of senseperception receives a great development. A complex object becomes mentally separated into a plurality of partial aspects, each of which can form a startingpoint for a series of comparisons, giving rise to different series of graduated resemblances such as those of pitch and loudness, and objects which are far apart in one series will be close together in another. To each of the different series there corresponds an abstract character or attribute of the object consciously distinguished from other abstract characters or attributes. Thus the category of Thinghood assumes a new form in ideational thinking from that which attaches to it in perceptual. The unity of the thing is distinguished from the plurality of its qualities, and that kind of predication becomes possible which is embodied in Language. The necessity of doing one thing at a time has led us to describe the nature and progress of comparison without reference to the use of language. But in fact the ideational activity which comparison involves could not proceed far unless it were guided and supported by expressive signs, i.e. signs directly expressing ideas and their relations. The nature, function, and origin of these signs is the topic which will next occupy us.