6. In considering Relation we must enquire whether it possesses the community of a genus, or whether it may on other grounds be treated as a unity.
Above all, has Relation — for example, that of right and left, double and half — any actuality? Has it, perhaps, actuality in some cases only, as for instance in what is termed “posterior” but not in what is termed “prior”? Or is its actuality in no case conceivable?
What meaning, then, are we to attach to double and half and all other cases of less and more; to habit and disposition, reclining, sitting, standing; to father, son, master, slave; to like, unlike, equal, unequal; to active and passive, measure and measured; or again to knowledge and sensation, as related respectively to the knowable and the sensible?
Knowledge, indeed, may be supposed to entail in relation to the known object some actual entity corresponding to that object’s Ideal Form, and similarly with sensation as related to the sense-object. The active will perform some constant function in relation to the passive, as will the measure in relation to the measured.
But what will emerge from the relation of like to like? Nothing will emerge. Likeness is the inherence of qualitative identity; its entire content is the quality present in the two objects.