From my son’s blog, Kierkegaard in Me, I’ve learned the word quiddity: the quality that makes a thing what it is; the essential nature of a thing. 2. a trifling nicety of subtle distinction, as in argument. (Unless noted, definitions here are from Dictionary.com.)
It describes properties 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 them to be this individual, and no other.
Tom used quiddity thusly:
If . . . you mean that I had a hand in the creation of these posts, or inspired their genesis, or even in some sense authored them myself—this too, I cannot deny, for all of us merely in the act of reading said writings gave them connotation and skin, hence substance, hence quiddity.
That post, which portrayed him in mock trial for his cheeky blogging about his professors, was pawky: (adj.) Chiefly British: Shrewd and cunning, often in a humorous manner; cunning; sly.