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The term "quiddity" derives from the Latin word quidditas, which was used by the medieval scholastics as a literal translation of the equivalent term in Aristotle's Greek to ti en einai (τὸ τί ἦν εἶναι) or "the what it was to be (a given thing)".
Quiddity describes properties that a particular substance (e.g. a person) shares with others of its kind. The question "what (quid) is it?" asks for a general description by way of commonality. This is quiddity or "whatness" (i.e., its "what it is"). Quiddity was often contrasted by the scholastic philosophers with the haecceity or "thisness" of an item, which was supposed to be a positive characteristic of an individual that caused it to be this individual, and no other. It is used in this sense in British poet George Herbert's poem, "Quiddity".