In Charles Peirce's ‘Logic of Relatives’ (1883), we see a move towards an understanding of terms as functions. One problem with traditional term logic is that it lacks the ability to deal with relations. Peirce's logic of relatives is meant to remedy that.  He adds terms to Boolean algebra that represent relations, and gives an extensional interpretation of them. They are not propositional functions in the full sense. Peirce's relatives are ‘common names’ that represent classes of pairs of objects (1883, 328). Thus, the logic of relatives represents a generalization of traditional logic rather than a departure from it.