In scholastic philosophy, quiddity [kwid-i-tee] was another term for the essence of an object, literally ‘what it is’ or its ‘whatness.’ The term derives from the Latin word ‘quidditas,’ meaning ‘what it was to be (a given thing),’ which was used by the medieval scholastics as a literal translation of the equivalent term in Aristotle’s Greek. It 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.
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 them to be this individual, and no other. It is used in this sense in British poet George Herbert’s eponymous poem, ‘Quiddity.’ In law, the term is used to refer to a quibble or academic point. An example can be seen in Hamlet’s graveside speech: ‘Where be his quiddities now, his quillets, his cases, his tenures’ says Hamlet, referring to a lawyer’s quiddities.
The Daily Omnivore 