 In “An Improvement in Boole’s Calculus of Logic” (1867) Peirce hints at the need for an improvement of Boolean logic, not in the context of predicate logic, but in its inability to express existential statements in the context of term logic. His 1870 paper “Description of a Notation for the Logic of Relatives, Resulting from an Amplification of the Conceptions of Boole’s Calculus” (DNLR) reveals his ambition to marry Boole’s algebraic notation with De Morgan’s effort at relational representation. Many agree that this paper introduces essential vocabulary of first-order predicate logic for the first time in history. Subsequently, in “On the Algebra of Logic” (1880) Peirce investigates two kinds of operations over relations—relative sum and relative product—and “The Logic of Relatives” (known as “Note B”) published in his edited book Studies in Logic by Members of the Johns Hopkins University (1883) shows a major progress in quantification, influenced by the work of O. H. Mitchell (who was his student). Finally, Peirce’s 1885 paper “On the Algebra of Logic: A Contribution to the Philosophy of Notations” has been considered to be the place where Peirce fully presented his quantification theory.