Up until 411, Augustine was involved in the controversy with the Donatists. Immediately after his conversion, Augustine believed that there were only two philosophical questions, one concerning the soul and the other concerning God. The first problem regarding the soul Augustine faced after his conversion was that of immortality. In De libero arbitrio, Augustine admits four hypotheses regarding the souls of the descendants: they derive from Adam's soul; they are created in time for every single man who is born; they pre-exist in God, who sends them to vivify the bodies of individuals; and they pre-exist 'somewhere else' and come into bodies spontaneously. Augustine's philosophia rationalis begins with a refutation of Academic Scepticism. The starting point of Augustine's ethics is an axiom taken from Cicero's Hortensius. Augustine carried out the task assigned to 'true philosophy' at Cassiciacum systematically in De Trinitate many years later. Augustine devoted three of the four books De doctrina christiana expressly to biblical hermeneutics.