Sui generis
In local government, a "sui generis" entity is one that does not fit with the general scheme of local governance of a country. For example in England, the City of London and the Isles of Scilly are the two "sui generis" localities, as their forms of local government are both (for historical or geographical reasons) very different from those of elsewhere in the country. 
In a press conference during which reporters were trying to analyse his political personality, Huey Long said, "...say that I am "sui generus", and let it go at that."
Abductive reasoning
In 1867, Peirce's "The Natural Classification of Arguments", hypothetical inference always deals with a cluster of characters (call them "P′, P′′, P′′′," etc.) known to occur at least whenever a certain character ("M") occurs. Note that categorical syllogisms have elements traditionally called middles, predicates, and subjects. For example: All "men" [middle] are "mortal" [predicate]; "Socrates" [subject] is a "man" [middle]; ergo "Socrates" [subject] is "mortal" [predicate]". Below, 'M' stands for a middle; 'P' for a predicate; 'S' for a subject. Note also that Peirce held that all deduction can be put into the form of the categorical syllogism Barbara (AAA-1).