In his Christian Theology and Natural Science, E. L. Mascall refers to a criticism by Elizabeth Anscombe of C. S. Lewis's well-known argument against determinism that appears in his Miracles. Both Lewis's argument and Anscombe's response appeared originally as papers delivered in the 40s to the Oxford Socratic Club. A certain historical interest attaches to that exchange in that Lewis seems to have been ‘deeply disturbed’ by it.2 I think he need not have been. But, more importantly, the sequence of Lewis's article followed by Anscombe's reply and then Mascall's comments on both, provides a suggestive presentation and examination of a certain kind of argument against determinism. Essentially it is a negative rebuttal of a retortive kind, such as Aristotle uses against the sceptic in the Metaphysics. But its treatment by these three writers indicates a metaphysical insight that could possibly furnish a positive refutation of any kind of radical determinism.