80 PSYCHOLOGY synthesis of thought, on the other hand, he symbolizes by forms such as the following : AB AB CD AB C &c. In explanation of this law as a law of intellection it is hardly sufficient to rest it ultimately on the fact " that in a given moment of time only a single act of apperception is possible." l This applies to all syntheses alike. ^ The point surely is that the one thing attended to in an intel- lective act is the synthesis of two things, and of two things only, because, as only one movement of attention is possible at a time, only two things at a time can be synthesized. In that merely associative synthesis by which the memory- continuum is produced attention moves from A to B and thence to C without any relation between A and B being attended to at all, although they must have relations, that of sequence, e.g., at least. The intellective synthesis which follows upon this first resolves the A~B into its elements, and then, if there be any ground for so doing, re-synthesizes them with a consciousness of what the syn- thesis means. 2 Formal Passing now to the remaining formal categories Differ- cate- ence, Likeness, Identity all of which come under the law gories. Q f Duality so far as they imply not a single presentation but some relation between two presentations, we have to seek out the characteristics of the states of mind in which these relations become objects of consciousness. The so- called fundamentum relationis, of course, can be nothing but the two presentations concerned. Just as certain, however, is it that the relation itself involves something more than these. Two equal triangles may be made to coincide, but are not necessarily coincident : Dromio of Ephesus might be mistaken for Dromio of Syracuse, but at least they never mistook each other. And this brings us to the point. As Lotze puts it, " Two impressions a and b are never to be regarded as more than stimuli which, by affecting the conscious subject in its very nature in- dividual and sui generis incite to reaction that activity by means of which there arise the new presentations, such as similarity, equality, contrast, &c." 3 The activity thus stimulated is what in other words we call the voluntary concentration of attention ; to ascertain, then, what these " new presentations " of difference, likeness, and so forth are, we must analyse carefully what takes place when two impressions a and 6 are expressly compared. Differ- " Difference," says Hume, " I consider rather as a nega- ence tion of relation than as anything real or positive. Differ- ence ^ Q tw() k m( j Sj ^ O pp OS ed either to identity [unity?] or resemblance. The first is called a difference of number, the other of kind." The truth seems rather to be that difference in the sense of numerical difference is so far an element in all relations as all imply distinct correlatives. To this extent even identity or at least the recognition of it rests on difference, that form of difference, viz., which is essential to plurality. But absolute difference of kind may be considered tantamount not, indeed, to the negation, but at least to the absence, of all formal relation. That this absolute difference or disparateness, as we may call it affords no ground for relations becomes evident when we consider (1) that, if we had only a plurality of absolutely different presentations, we should have no con- sciousness at all (comp. p. 45) ; and (2) that we never com- pare although we distinguish, i.e., recognize, numerical andlike- 1 Wundt, op. cU., i. p. 58. 3 It need not, of course, be maintained that in every act of thought, no matter how abstract, the ideas related have been previously con- nected by association. But certainly at the outset this is the case, in such wise that all the forms of intellectual synthesis are prefigured in the connexions of the ideational train or its reduplications. 3 Qrundziige der Psychologic, p. 24. difference where presentations seem absolutely or totally different, as are, e.g., a thunderclap and the taste of sugar, or the notion of free trade and that of the Greek accusative. All actual comparison of what is qualitatively different rests upon opposition or contrariety, i.e., upon at least partial likeness (comp. p. 46). This being understood, it is note- worthy that the recognition of such unlikeness is, if any- thing, more " real or positive " than that of likeness, and is certainly the simpler of the two. In the comparison of sensible impressions as of two colours, two sounds, the lengths or the directions of two lines, &c. we find it easier in some cases to have the two impressions that are com- pared presented together, in others to have first one pre- sented and then the other. But either way the essential matter is to secure the most effective presentation of their difference, which in every case is something positive and, like any other impression, may vary in amount from bare perceptibility to the extremest distance that the continuum to which it belongs will admit. Where no difference or distance at all is perceptible, there we say there is likeness or equality. Is the only outcome, then, that when we pass from ab to ac there is a change in consciousness, and that when ab persists there is none ? To say this is to take no account of the operations (we may symbolize them as etc - ab cb, ab ab = 0) by which the difference or the equality results. The change of presentation (be) and absence of change (0) are not here what they are when merely passive occurrences, so to put it. This is evident from the fact that the former is but a single presentation and the latter no presentation at all. The relation of unlikeness, then, is distinguished from the mere "position" of change by (1) the voluntary concentration of attention upon ab and ac with a view to the detection of this change as their difference, and by (2) the act, relating them through it, in that they are judged unlike to that extent. The type of comparison is such superposition of geometrical lines or figures (as, e.g., in Euclid I. iv.) : if they coincide we have concrete equality ; if they do not their difference is a line or figure. All sensible comparisons conform essentially to this type. In comparing two shades we place them side by side, and passing from one to the other seek to determine not the absolute shade of the second but its shade relative to the first, in other words, we look out for contrast. We do not say of one " It is dark," for in the scale of shades it may be light, but "It is darker "; or vice versa. Where there is no distance or contrast we simply have not two impressions, and, as said if we consider the difference by itself no impression at all. Two coincident triangles must be perceived as one. The distinction between the one triangle thus formed by two coinciding and the single triangle rests upon something extraneous to this bare pre- sentation of a triangle that is one and the same in both cases. The marks of this numerical distinctness may be various : they may be different temporal signs, as in re- duplications of the memory-continuum ; or they may be constituents peculiar to each, from which attention is for the moment abstracted, any one of which suffices to give the common or identical constituent a new setting. In general, it may be said (1) that the numerical distinctness of the related terms is secured in the absence of all qualita- tive difference solely by the intellectual act which has so unified each as to retain what may serve as an individual mark ; and (2) that they become related as " like " either in virtue of the active adjustment to a change of impres- sion which their partial assimilation defeats, or in virtue of an anticipated continuance of the impression which this assimilation confirms. It is in keeping with this analysis that we say in common Idenl speech that two things in any respect similar are so far the same ; that, e.g., the two Dromios
