Haecceity and thisness

A ‘haecceity’ (from the Latin, haecceitas, which translates literally as ‘thisness’) is a certain kind of property. In broad outline, a thisness is a primitive, particular, nonqualitative property of an individual, i.e. the property of being a specific individual (or, perhaps, the property of being identical with a specific individual). For example, Ruth Barcan Marcus’s thisness is the property being (identical with) Ruth Barcan Marcus, and so on for all individuals. To clarify: although it is typical to see a thisness described as the property of being identical with an individual, it is not merely the property of being self-identical, which all individuals exemplify trivially; it is a special kind of property that is uniquely exemplified by its bearer. And so, for any individual x, since the property being (identical with) x is both uniquely exemplified by x and essential to x, so x’s thisness is a nonqualitative individual essence of x.

The terminology of ‘haecceity’ and ‘thisness’ derives from the work of John Duns Scotus (c.1266–1308) and some of Scotus’s insights and application of thisnesses are still relevant to debates about identity and individuation. This terminology has its roots in the scholastic philosophy of the High Middle Ages and it was revived in contemporary metaphysics by the work of Robert Merrihew Adams in the second half of the 20th century. In addition to the question of what is the metaphysical nature of a thisness, a considerable amount of the debate concerns what thisnesses can do to ‘earn their keep’ in a systematic metaphysics. Some say that accepting an ontology of thisness permits the individuation of qualitatively indiscernible objects or events – with appropriate footnotes to Scotus. Others say that accepting a specific ontology of thisness allows one to defend certain positions in the philosophy of time, i.e. the growing block theory of time, or presentism.

We are concerned here with haecceities (thisnesses) and not ‘haecceitism’, the view that a world could not be nonqualitatively different without a qualitative difference.