 First proposed by John Duns Scotus (1266–1308), a haecceity is a non-qualitative property responsible for a substance’s individuation and identity. As understood by Scotus, a haecceity is not a bare particular underlying qualities. It is, rather, a non-qualitative property of a substance or thing: it is a “thisness” (a haecceitas, from the Latin haec, meaning “this”) as opposed to a “whatness” (a quidditas, from the Latin quid, meaning “what”) – akin to what are sometimes known in recent philosophy as “suchnesses.” The origins of the proposal have both philosophical and theological components. In 1277, the Bishop of Paris, Stephen Tempier, condemned the view that there could not be more than one angel in a given species. The condemned view was held by Christian Aristotelians in the thirteenth century – pre-eminently, Thomas Aquinas – and originated in the claim that intra-specific individuation is in some sense through different lumps of matter. As immaterial substances, angels cannot be individuated in this way. And in any case, as immaterial and non-spatial, angels seem to be good candidates for possibly lacking any kind of qualitative difference. Hence, as it is possible that two angels be exact replicas of each other, angels are good cases for testing intuitions related to the identity of indiscernibles, and thus the question of individuation.