Book VII, Chapter 2

Augstine presents an argument against the Manichaes that had been presented to him by his friend Nebridius. For Augustine, this was the decisive and final argument with which to reject them. As with most of Augustine's spiritual development, his emotional drive (antipathy of the Manichaes) precedes his intellectual resolution (intellectual rejection of Manichaen doctrine). Indeed, it is the emotional energy and desire--the restless heart-- that pushes him on to intellectual formation.

According to the Manichaes, at least some part of God can become contaminated by evil; yet, God is incorruptible, which makes the Manichaen assertation a contradiction. I follow Nebridius's argument, but it may require more knowledge than I have, to understand the internals of the argument in depth.