[3] Schmidkunz, _loc. cit._ This author, who rightly insists upon the positive character of abstraction (which is too frequently considered as a negation) observes that no concept, not even that of infinity, is in its psychological genesis the result of negation, for, “in order to deduce from the idea of a finite thing the idea of infinity, it is first necessary to abstract from that thing its quality of finality, which is certainly a positive act; subsequently, in order to reach infinity, it is sufficient either constantly to increase the time, magnitude, and intensity of the finite, which is a positive process; or to deny the limits of the finite, which is tantamount to denying the negation.” [4] _Psychology of Attention._ Chicago: The Open Court Publishing Co. [5] See especially Hoeffding, _Psychologie_. German translation. Second Edition, pp. 223 et seq. [6] W. James, _Psychology_. Vol. I., p. 459. [7] Herbert Spencer, _Principles of Psychology_. Vol. I., Part 2, Chapter II.—Bain (in the last chapter of _Emotions and Will_) says that nothing more fundamental can possibly be assigned as a mark of intelligence than the feeling of difference between consecutive or co-existing impressions. “There are cases, however, where agreement imparts the shock requisite for rousing the intellectual wave; but it is agreement so qualified as to be really a mode of difference.” For a review and ample discussion of this problem see Ladd’s _Psychology, Descriptive and Explanatory_, Chapter XIV. The earlier psychologists, in considering the “faculty of comparison” which acts by resemblance and difference, as primordial, had observed the same fact, although they described it in different terms. [8] W. James, _Psychology_. Vol. I., pp. 502 and 506.