Were there space we might go on to point out how this law of life is traceable, not only in the origin but in the development of language; how in primitive tongues the plural is made by a duplication of the singular, which is a multiplication of the word to make it like the multiplicity of the things; how the use of metaphor—­that prolific source of new words—­is a suggesting of ideas that are like the ideas to be conveyed in some respect or other; and how, in the copious use of simile, fable, and allegory among uncivilised races, we see that complex conceptions, which there is yet no direct language for, are rendered, by presenting known conceptions more or less like them.

This view is further confirmed, and the predominance of this notion of likeness in primitive times further illustrated, by the fact that our system of presenting ideas to the eye originated after the same fashion.  Writing and printing have descended from picture-language.  The earliest mode of permanently registering a fact was by depicting it on a wall; that is—­by exhibiting something as like to the thing to be remembered as it could be made.  Gradually as the practice grew habitual and extensive, the most frequently repeated forms became fixed, and presently abbreviated; and, passing through the hieroglyphic and ideographic phases, the symbols lost all apparent relations to the things signified:  just as the majority of our spoken words have done.

Observe again, that the same thing is true respecting the genesis of reasoning.  The likeness that is perceived to exist between cases, is the essence of all early reasoning and of much of our present reasoning.  The savage, having by experience discovered a relation between a certain object and a certain act, infers that the like relation will be found in future cases.  And the expressions we constantly use in our arguments—­“analogy implies,” “the cases are not parallel,” “by parity of reasoning,” “there is no similarity,”—­show how constantly the idea of likeness underlies our ratiocinative processes.

Still more clearly will this be seen on recognising the fact that there is a certain parallelism between reasoning and classification; that the two have a common root; and that neither can go on without the other.  For on the one hand, it is a familiar truth that the attributing to a body in consequence of some of its properties, all those other properties in virtue of which it is referred to a particular class, is an act of inference.  And, on the other hand, the forming of a generalisation is the putting together in one class all those cases which present like relations; while the drawing a deduction is essentially the perception that a particular case belongs to a certain class of cases previously generalised.  So that as classification is a grouping together of like things; reasoning is a grouping together of like relations among things.  Add to which, that while the perfection gradually achieved in classification consists in the formation of groups of objects which are completely alike; the perfection gradually achieved in reasoning consists in the formation of groups of cases which are completely alike.