The Commens Dictionary
Quote from ‘On the Logic of Quantity’
Dual relations, – facts about pairs of subjects, – are of two types, first those which imply no more about their subjects that that they have certain qualities between which some comparison is made; and secondly, those which imply more about their subjects than is true of them in their separate existences, something real and positive which could not be true of one if the other did not exist to enable it to be true, in other words a real action and reaction between the individuals. This is the old distinction between real relations and relations of reason. Real relations exhibit the fully developed type of duality. In this case, it is what happens to the individuals, the actions of them, which pairs them. Relations of reason imply no other facts than the possession of two qualities severally by two individuals; and it is primarily the qualities that are paired.