The usual story about Augustine's doctrine of divine illumination, which lies at the centre of his theory of knowledge, is that it lasted until Bonaventure, the great Franciscan contemporary of Aquinas, but was rejected by the later Franciscan tradition beginning with Duns Scotus, thus ushering in more secularised views of knowledge in modernity. For many Christian historians, especially Catholics, this is a story of decline and loss, as Scotus initiates a passage to modernity in which knowledge and reason itself are cut off from their roots in the truth of God.

Lydia Schumacher tells a different story. In her new book she argues that Aquinas was a more faithful heir of Augustine's doctrine of illumination than Bonaventure, so that what the later Franciscans rejected was not really Augustine's theory at all. According to this story, what we find in Bonaventure is more Arabic than Augustinian, based on an appropriation of Avicenna's view of extrinsic illumination – as if the divine light interfered with the human mind and imposed ideas on it from above. It was Aquinas who preserved Augustine's view of intrinsic divine illumination, precisely by updating it in terms of contemporary Aristotelian psychology. Schumacher concludes by proposing a future for Augustine's theory of knowledge which follows Thomas’ example by updating Augustine for today.

There are reasons to welcome this story. The old way of contrasting Augustinian and Aristotelian strands of medieval thought is surely too simple, especially in the case of Aquinas. And it is certainly important to see that Bonaventure's notion of illumination is not merely Augustine's, but reflects distinctive concerns of his own. Most of all, the possibility that the late-medieval rejection of divine illumination did not simply represent the failure of Augustinianism has great appeal.

Yet Schumacher's story is not without its problems. Too many motives of the old story remain: as if modernity could be blamed on the epistemology of a few Franciscan professors, or as if we needed to pick either Aquinas or Bonaventure to be our hero. And while Schumacher does well to read Augustine's theory of knowledge in the context of his most sophisticated theological work, especially the great treatise On the Trinity where illumination is taken up into the project of restoring the image of God in us, her tendency to treat Augustine's thought as if it were theological rather than philosophical seems to me wrong-headed – as if Neo-Thomist efforts to keep these two modes of inquiry in distinct domains could make sense of Augustine's much more seamless thinking.

In many ways the problems begin with the title. The old notion that Augustine has a theory of illumination has never squared with his actual language which, like the Platonist tradition from which he drew, tends to speak of vision rather than illumination. Heeding Augustine's own language here can set to rest the worry that he makes the human mind into a passive recipient of forms imposed from outside. ‘Illumination’ suggests a divine light invading the mind, whereas Platonist talk of intellectual vision suggests instead an active mind with the power to see the truth, looking for the light and finding it. Taking Augustine's Platonism seriously thus affords a better understanding of Augustine's theory of knowledge than taking either Aristotelian or Avicennan notions of the intellect as normative. Contemporary theologians have often missed the integrity as well as the excitement and danger of Augustine's thought by downplaying the depth of his theological appropriation of Platonism.