Sui generis
A similar case that led to the use of the label "sui generis" is the relationship of New Caledonia relative to France, because the legal status of New Caledonia can aptly be said to lie somewhere between a French overseas collectivity and a sovereign nation. Although other examples of such status for other dependent or disputed territories may exist, this arrangement is unique within the French realm.
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).