In “Divine Foreknowledge and Facts” Paul Helm defends a traditional argument to the incompatibility of foreknowledge and free will “against the attempts of Kenny and some other recent writers to provide a reconciliation.” I shall here set out a reconciliationist position similar to those he attacks, but innocent of the charges he makes against them.

The argument, discussed by St. Thomas in the Summa Theologiae, employs the doctrine of the necessity of the past to show that literally prior knowledge of a free action is impossible. Since prior knowledge of an action is past relative to the ·action, the fact of that knowledge is necessary. It is a past fact, and so cannot be undone. From this it follows that the action itself must be necessary; for necessity is transitive, and knowledge of p implies p. But only contingent actions can be free, and so no free action can be foreknown.