We can say many things about order in time because we understand the word 'precede', although we cannot enumerate all the couples x, y such that x precedes y. There is, however, a further argument against the view of relations as classes of couples: the couples have to be ordered couples, that is to say, we must be able to distinguish the couple x, yfrom the couple y, x. This cannot be done except by means of some relation in intension. So long as we confine ourselves to classes and predicates, it remains impossible to interpret order or to distinguish an ordered couple from a class of two terms without order.
Source: My Philosophical Development, 1959, by Bertrand Russell
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