Identity and identities: the metaphysics and semantics of 'qua'

One of the most fundamental principles in the logic of identity is Leibniz’s Law: if a and b are identical, then any property had by a is also had by b. But this logical notion of identity would appear to be in tension with our ordinary understanding of the multifaceted identities of individuals. For it is quite common for a single individual to have multiple functions, roles, or identities and have different, even incompatible properties in these different roles or capacities. For instance, when a judge is also the referee of a football club, it is possible for the judge to be corrupt while the referee is uncorrupt. When a father is also a literary critic, it is possible for the father to be kind while the critic is cruel. And when, like Duchamp’s piece Fountain, a urinal is also an artwork, it is possible for the urinal to be ordinary while the artwork is extraordinary. Cases with this structure are not uncommon, yet they would appear to provide counterexamples to Leibniz’s Law. A standard response amongst philosophers is to invoke qualifications with ‘as’ or ‘qua’: The person is corrupt qua judge but uncorrupt qua referee. The person is kind as a father but cruel as a critic. Fountain is ordinary qua urinal, but extraordinary qua work of art. Despite the prominence of this response, there is next to no systematic literature on how such qualifications work and how precisely they help reconciling cases such as the above with Leibniz’s Law. To fill this lacuna, this dissertation investigates the metaphysics, semantics, and logic of qualification. I develop and assess four initially plausible proposals for how a satisfactory solution to the puzzle cases can be reconciled with (some version of) Leibniz’s Law using qualifications with ‘as’ or ‘qua’, and I argue that all but one are unsatisfactory. I go on to develop the remaining approach to qualification into a detailed theory, and I show that my theory of qualification affords an illuminating way of negotiating the tensions between identity, the simple well-behaved relation everything bears to itself and only itself, and identities, the categories we live by