 What then, according to Locke, is it to have the same consciousness as some past person? He is customarily interpreted as holding that person A is the same person as earlier person B just in case A is able to remember enough of what happened to B. This is sometimes referred to as the memory criterion of personal identity. The memory criterion was criticized by Butler and Reid principally because it was said to be circular, and, as a criterion of personal identity, incompatible with the transitivity of identity. (See Section 2.2, and Joseph Butler ‘Of Personal Identity’ and Thomas Reid ‘Of Mr. Locke's Account of Our Personal Identity’ in Perry 1975.)