By the term 'soul' (anima) Augustine meant the highest immaterial element in man, the art of man to which mind (mens, more rarely animus) is but a function. Exactly what 'soul' is and how God creates souls he regarded as beyond human knowledge. It would make for simplicity, he once remarked apropos of infant baptism, if all Adam's posterity derived souls as well as bodies from their first parent by heredity. But this doctrine (traducianism) that souls are acquired by heredity carried more physical implications than at least some Platonists could feel at ease with. Perhaps it would be preferable to say that God expressly creates a soul for each individual as conceived. [Augustine ignored as silly the objection that the Creator should be spared endless fuss.] Or, more platonically, all souls exist in God from the first, and are either sent or even choose to come and inhabit bodies on earth. Neoplatonic philosophers disagreed among themselves on the correct answer, and the Bible offered no guidance. In Augustine's mind none of these options could be finally excluded. His refusal to give a decision incurred sharp criticism from some who felt that such a question simply could not be left in the limbo of indecision. He remained unmoved.
--Augustine, by Henry Chadwick. Oxford University Press, 1986, p. 49-50.