Note 386 — Chapter XII

There are two other 'principles of identity' in philosophy. The ontological one asserts that every real thing is what it is, that a is a, and b, b. The logical one says that what is once true of the subject of a judgment is always true of that subject. The ontological law is a tautological truism; the logical principle is already more, for it implies subjects unalterable by time. The psychological law also implies facts which might not be realized: there might be no succession of thoughts; or if there were, the later ones might not think of the earlier; or if they did, they might not recall the content thereof; or, recalling the content, they might not take it as 'the same' with anything else.