The Commens Dictionary
Quote from ‘Definitions for Baldwin's Dictionary [R]’
Relation [L. relatio, a report. from refero, to carry back.] A fact concerning a set of objects, called the relates, or a generalization of a class of such facts. A relation is dyadic, triadic, etc. according to the number of relates. When the set is a pair, the relates are commonly distinguished as relate and correlate, and the fact is stated as something being true of the former, with a subordinate regard for the latter. This is, of course, due to the fact that in most languages the noun denoting relate is put in the nominative case, while the correlate is put in an oblique case, usually the accusative.Many languages do this even with such a verb as “is”. There are languages which do not give so much prominence to one relate over the other or others; and put the subject in an oblique case. The Gaelic commonly does so. Still, there must be some syntactical provision to distinguish in what order of arrangement the set of subjects has the predicate asserted of it.