 There may seem to be an obvious objection to the employment of transworld identity to interpret or paraphrase statements such as ‘Bertrand Russell could have been a playwright’ or ‘George Eliot might have been a scientist’. A fundamental principle about (numerical) identity is Leibniz’s Law: the principle that if A is identical with B, then any property of A is a property of B, and vice versa. In other words, according to Leibniz’s Law, identity requires the sharing of all properties; thus any difference between the properties of A and B is sufficient to show that A and B are numerically distinct. (The principle here referred to as ‘Leibniz’s Law’ is also known as the Indiscernibility of Identicals. It must be distinguished from another (more controversial) Leibnizian principle, the Identity of Indiscernibles, which says that if A and B share all their properties then A is identical with B.) However, the whole point of asserting a transworld identity is to represent the fact that an individual could have had somewhat different properties from its actual properties. Yet does not (for example) the claim that a philosopher in the actual world is identical with a non-philosopher in some other possible world conflict with Leibniz’s Law?