 The view that an individual’s transworld identity is ‘bare’ is sometimes described as the view that its identity consists in its possession of a ‘haecceity’ or ‘thisness’: an unanalysable non-qualitative property that is necessary and sufficient for its being the individual that it is. (The term ‘individual essence’ is sometimes used to denote such a haecceity. It should be noted that according to the terminology used in this article, although a haecceity would be an individual essence, it would not be a non-trivial individual essence.) However, it is not obvious that the belief in bare identities requires the acceptance of haecceities. One can apparently hold that transworld identities may be ‘bare’ without holding that they are constituted by any properties at all, even unanalysable haecceities (cf. Lewis 1986, 225; Adams 1979, 6–7). Thus we should distinguish what is standardly known as ‘haecceitism’ (roughly, the view that there may be bare identities across possible worlds in the sense of identities that do not supervene on qualitative properties) from the belief in haecceities (the belief that individuals have unanalysable non-qualitative properties that constitute their being the individuals that they are). (For more on the use of the term ‘haecceitism’ see Lewis 1986, Ch. 4, Section 4; Adams 1979; Kaplan 1975, Section IV; also the separate entry on Haecceitism. For the history of the term ‘haecceity’, see the entry on Medieval Theories of Haecceity.)