I have been reading City of God online edition lately, and I was pretty concerned upon starting that the thing was going to be an epic slog through swampy jargon-infested waters. I have read the first five books (out of twenty-two) and so far my fears were entirely unwarranted. St. Augustine is a very good and engaging writer, and the translation I am reading is excellent. In Book V (among other things) he attacks the idea of fate (by which some antagonists claimed that Rome’s empire was assured) and defends the Christian view:
[W]e assert both that God knows all things before they happen and that we do by our free will everything that we feel and know would not happen without our volition. (V.9)
Some people think that St. Augustine held such a strong view of divine sovereignty as to preclude any genuine free human will. On the contrary. He affirmed both. This line was taken up by Thomas Aquinas centuries later, who affirmed that God causes to happen those things which are to happen by free will to actually occur by free will. This is the greatness and mystery of divine providence and purpose in the world. Our choices are never meaningless and they are never a surprise to God.
In a passage in which he briefly describes the living and true God in contrast to the false gods of Rome, St. Augustine includes the following remarks about divine providence and free will.
He directs the whole of his creation, while allowing to his creatures the freedom to initiate and accomplish activities which are their own; for although their being completely depends on him, they have a certain independence. (City of God VII.30, available online here; quotation is from this translation)
The saint attributes a certain sort of freedom not just to men but to all creatures, “to initiate and accomplish activities which are their own”. We do not attribute a dog’s bite to God; we attribute it to the dog, for the reason St. Augustine says. In the same way man exercises free will because it is part of what it means to be human, and the things that we do can only rightly be said to be ours to the extent that we freely and deliberately choose them.