Abstract: Leibniz denied, famously, that any possible individual exists in more than one possible world, so that a man who in fact never marries could not have married and still been himself. He claimed that this follows from his thesis that the predicate of every true affirmative proposition is contained in some way in the concept of its subject and his associated thesis that the definitive concept of each individual substance is complete. This chapter argues that the purely formal aims of logical theory involved in the predicate containment and complete concept theses do not in fact require the denial of counterfactual or transworld identity.

Keywords: counterfactual, identity, Leibniz, logical theory, possible world, transworld identity,