[77] Wundt (_Logik_, I., pp. 113 et seq.) gives what he regards as a complete classification of concepts, but it does not correspond with our design. It may be summarised as follows. Four classes: I. Identical or equivalent concepts; Aristotle = Alexander’s tutor. II. Subordinate or superordinate concepts; mammals and vertebrates, etc. III. Co-ordinated concepts, comprising five species: i. Disjunctive concepts; sound and noise, French and German, etc. They are subordinate to a larger concept. ii. Correlative concepts, with reciprocal relations; men and women, mountain and valley. iii. Contrary concepts; high and low, good and bad. iv. Contingent concepts; such, i. e., as touch, with very minute, perceptible differences; this highly important category comprises numbers. v. Interferent concepts, which coincide or partially cross; negro and slave, rectangle and parallelogram. IV. Concepts which are interdependent; etc., space and movement, crime and punishment, demand and supply, labor and wages. This table may suit the logician but not the psychologist, because it presents the concepts under what may be termed the static order, i. e., ready formed: we, on the other hand, are considering them as dynamic, i. e., in their becoming and order of genesis. [78] For details, with quotations in point, consult Agassiz: _De l’espèce_, Chap. III., and E. Perrier, _La Philosophie zoologique avant Darwin_, Chap. II. [79] Agassiz, _op. cit._, gives a summary of the successive improvements. They are of interest not merely to the zoölogist, but also from our own point of view, as showing the increasing preponderance of analysis, and search for fundamental characteristics, to the exclusion of the external resemblances which served as basis for the more primitive classifications. [80] Under the heading “Observations on General Terms” the _American Journal of Psychology_, III. i, p. 144 (Jan., 1890) gives the results of an investigation conducted upon 113 school children aged 13 to 18. The words _being_, _the infinite_, _literature_, _abstraction_, _number_, _play_, _coldness_, _horror_, etc., were written down, and a few moments were given the pupils to transcribe their impressions in each case. The summarised answers are not devoid of interest, but the object of the inquiry is evidently very different from our own. [81] The word “law” was purposely chosen for its ambiguity; physical laws, moral or social laws. The immense majority of answers were in the juristic sense. Ex., Code, Law of the Twelve Tables, a judge, woman with scales, etc. [82] For the word _infinity_, those who fall under this type see the printed word, or the mathematical sign ∞. [83] It should be noted that he lived among these animals and experimented with them almost daily.