  An important part of thirteenth-century psychology was the development of a theory of free action. This was especially important both for theology and for ethics. Medieval thinkers, beginning with Augustine, recognized that moral responsibility requires freedom and so the possibility of that freedom needed to be explained. Along those same lines, they argued that unless human beings are able to act freely, God is not justified in punishing sins. Furthermore, human freedom plays a major role in theodicy; for example, Augustine argues that God is not responsible for the evil found in the world because that evil is perpetrated by the free choices of human beings (De lib arb). Thus, given this background and these commitments, it was common for medieval philosophers to examine the topic of freedom somewhere in their writings. In the first half of the thirteenth century, it was customary to examine these issues in the context of a treatise on what became known as liberum arbitrium (see Kent 1995, McCluskey 2001). In medieval theories of action in the early part of the thirteenth century, “liberum arbitrium” is a technical term. It is a placeholder for whatever it is that enables human beings to act freely. The term originates in the work of Augustine who wrote a treatise entitled De libero arbitrio.  The starting point for thirteenth-century treatises on liberum arbitrium was a definition taken from Peter Lombard’s Sentences: “liberum arbitrium is a faculty of reason and will, by which good is chosen with the assistance of grace, or evil, when grace is not there to assist. And it is called ‘liberum’ with respect to the will, which can be turned toward either [good or bad], while [it is called] ‘arbitrium’ with respect to reason, as it has to do with that power or faculty to which the discerning between good and evil belongs.” Although Lombard’s main discussion of liberum arbitrium is found in book two, distinction twenty-five of his Sententiae in IV libris distinctae, this definition is found in the twenty-fourth distinction of book two, chapter three. This definition was commonly but mistakenly attributed to Augustine by commentators in the thirteenth century. Lombard himself does not reveal his source.  References to Augustine dominate his discussion of liberum arbitrium, which might account for the association of the definition with Augustine.