 And the tradition is also later enlarged by Scholastic theorists, most importantly Aquinas (Aquinas, Summa Theologica II, q.88 &amp; q.110). Aquinas used Aristotelian assumptions and techniques to expand and detail the theory, deriving the duty to keep a promise from the intentions of the promisor and the underpinning virtues (see Gordley 1991: 10ff).