indiscernibility of identicals the principle that if A and B are identical, there is no difference between A and B: everything true of A is true of B, and everything true of B is true of A; A and B have just the same properties; there is no property such that A has it while B lacks it, or B has it while A lacks it. A tempting formulation of this principle, ‘Any two things that are identical have all their properties in common’, verges on nonsense; for two things are never identical. ‘A is numerically identical with B’ means that A and B are one and the same. A and B have just the same properties because A, that is, B, has just the properties that it has. This principle is sometimes called Leibniz’s law. It should be distinguished from its converse, Leibniz’s more controversial principle of the identity of indiscernibles. A contraposed form of the indiscernibility of identicals – call it the distinctness of discernibles – reveals its point in philosophic dialectic. If something is true of A that is not true of B, or (to say the same thing differently) if something is true of B that is not true of A, then A and B are not identical; they are distinct. One uses this principle to attack identity claims. Classical arguments for dualism attempt to find something true of the mind that is not true of anything physical. For example, the mind, unlike everything physical, is indivisible. Also, the existence of the mind, unlike the existence of everything physical, cannot be doubted. This last argument shows that the distinctness of discernibles requires great care of application in intentional contexts. See also IDENTITY, INTENSIONALIT. D.H.S.