interdependent, may often be used without attending to their relativity, and may then be considered as Absolute.  We cannot say ’the hunter returned empty handed,’ without implying that ‘the prey escaped’; but we may say ‘the man went supperless to bed,’ without implying that ’the chamois rejoiced upon the mountain.’  Such words as ‘man’ and ‘chamois’ may, then, in their use, be, as to one another, non-relative.

To illustrate further the relativity of terms, we may mention some of the chief classes of them.

Numerical order:  1st, 2nd, 3rd, etc.; 1st implies 2nd, and 2nd 1st; and 3rd implies 1st and 2nd, but these do not imply 3rd; and so on.

Order in Time or Place:  before-after; early-punctual-late; right-middle-left; North-South, etc.

As to Extent, Volume, and Degree:  greater-equal-less; large-medium-small; whole and part.

Genus and Species are a peculiar case of whole and part (cf. chaps. xxi.-ii.-iii.).  Sometimes a term connotes all the attributes that another does, and more besides, which, as distinguishing it, are called differential.  Thus ‘man’ connotes all that ‘animal’ does, and also (as differentiae) the erect gait, articulate speech, and other attributes.  In such a case as this, where there are well-marked classes, the term whose connotation is included in the others’ is called a Genus of that Species.  We have a Genus, triangle; and a Species, isosceles, marked off from all other triangles by the differential quality of having two equal sides:  again—­Genus, book; Species, quarto; Difference, having each sheet folded into four leaves.

There are other cases where these expressions ‘genus’ and ‘species’ cannot be so applied without a departure from usage, as, e.g., if we call snow a species of the genus ‘white,’ for ‘white’ is not a recognised class.  The connotation of white (i.e., whiteness) is, however, part of the connotation of snow, just as the qualities of ‘animal’ are amongst those of ‘man’; and for logical purposes it is desirable to use ‘genus and species’ to express that relativity of terms which consists in the connotation of one being part of the connotation of the other.

Two or more terms whose connotations severally include that of another term, whilst at the same time exceeding it, are (in relation to that other term) called Co-ordinate.  Thus in relation to ‘white,’ snow and silver are co-ordinate; in relation to colour, yellow and red and blue are co-ordinate.  And when all the terms thus related stand for recognised natural classes, the co-ordinate terms are called co-ordinate species; thus man and chamois are (in Logic) co-ordinate species of the genus animal.