In 1867, Peirce's "", 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" are "mortal" [predicate; "Socrates" is a "man" [middle; ergo "Socrates" is "mortal" [predicate". Below, 'M' stands for a middle; 'P' for a predicate; 'S' for a subject. Peirce held that all deduction can be put into the form of the categorical syllogism Barbara (AAA-1).