This paper will be concerned with the antecedents of Aristotle's bipartite or moral psychology. It will consider two common theses: 1) Aristotle's bipartite psychology is in origin a popular psychology already present (if not clearly formulated) in Euripides' Medea; 2) Aristotle's bipartite psychology developed out of tripartition by collapsing together the two lower elements of tripartition. Roughly, I shall be affirming the first and rejecting the second thesis. In both cases I hope to develop and make more precise the origins of Aristotle's bipartite psychology.
Fortenbaugh, William W., "On the Antecedents of Aristotle's Bipartite Psychology" (1969). The Society for Ancient Greek Philosophy Newsletter. 187.