With such a combining agency we are familiar as our intelligence. It is through it that the sensation of the present moment takes a character from comparison with the sensation of a moment ago, and that the occurrence, consisting in the transition from one to the other, is presented to us. It is essential to the comparison and to the character which the sensations acquire from the comparison, essential, too, to their forming an observable event or succession, that one should not be fused with the other, that the distinct being of each should be maintained. On the other hand, in the relation to which their distinctness is thus necessary they are at the same time united. But if it were not for the action of something which is not either of them or both together, there would be no alternative between their separateness and their fusion. One might give place to the other, or both together might be combined into a third; but a unity in which their distinctness is preserved could not be constituted without the relating act of an intelligence which does not blend with either. (§ 29 ¶ 1)

The above is an instance of relation between sensations which, as brought into relation by intelligence, become sensible objects or events. But the same or an analogous action is necessary to account for any relation whatever—for a relation between material atoms as much as any other. Either then we must deny the reality of relations altogether and treat them as fictions of our combining intelligence; or we must hold that, being the product of our combining intelligence, they are yet empirically real on the ground that our intelligence is a factor in the real of experience; or if we suppose them to be real otherwise than merely as for us, otherwise than in the cosmos of our experience, we must recognise as the condition of this reality the action of some unifying principle analogous to that of our understanding. (§ 29 ¶ 2)