St Augustine develops his interpretation of moral evil in response to a plethora of contemporary opinions. He is familiar with the Platonic and Neoplatonic views that for man to run away from the true and the good and to succumb to the pleasures of the senses is to become ensnared by the world's attractiveness. The additional Neoplatonic position that matter was nearly nothing because not a definite being seems to have some influence on the notion of evil Augustine adopts. The Manicheans, for their part, had been so impressed with evil in the world that they maintained the existence of a supremely evil being along with a supremely good being. Man, according to their teaching, possessed a mixture of evil and good and, as a result, two wills, a good and an evil one. Finally, Scripture, both Old and New Testaments, repeatedly presented evil as a turning away from God and/or rejection of God's will.

In an early observation about moral evil, Augustine leads Evodius to the conclusion that moral evil stems from or lies in the will's wrong desire or lust (a general term for wrongful desire [cupiditas] pertaining to the senses). When he returns to the topic again in Books II and III of Free Decision of the Will he tries to identify just what accounts for the existence of evil in the will and what the nature of evil is.

He has by now formulated his basic notion, metaphysically grounded, of evil as 'the absence of good in a being'. This notion needs to be understood with precision. Here Augustine rejects the Manichean notion of evil by maintaining that evil can only exist in a being or in that which is good. He has also identified the highest reality in the universe, God, as being and as good. Evil cannot be a supreme being because of good's metaphysical precedence. There also cannot be two supremely good beings. But then how is it that evil actually does affect being?

Augustine goes on to describe this lack in the being of things as the lack of what normally speaking ought to be in a thing by nature. For example, a person born blind would display this sort of lack. However, this lack or absence of being does not always and necessarily mean something subtracted or omitted from a being. A thing may be deprived of what, normally speaking, its being or nature requires by way of excess. An overweight person would be a case in point.

This two-dimensional sense of absence (or lack in a being of what is normally good for it) suggests to Augustine that basically one is dealing with a disorder in the thing. Employing this refined sense of 'disorder' to explain a thing's lack of being places Augustine in a better position to treat of moral evil. Moral evil, in the human will, is a disorder, as wrong desire which inclines one to desire either something that one should not, an apparent good, or to desire ineffectively the means towards one's goal or a real good. He illustrates the first kind of disorder in an analysis of what occurs mentally in the case of a suicidal person.

The suicide seeks peace from what troubles him but mistakes death, as an imagined final state of non-being that will convey peace, for a genuine state of peace. Genuine peace, he notes, can only be realised by one who exists to enjoy it.

However, when it comes to the case of those who take an ineffective means to an end, he resorts to an evaluation of a perplexing phenomenon in life. Apparently all humans seek and will happiness, yet many fail to achieve this goal. If one's will is truly in one's power then this does pose a puzzling situation.

Augustine's procedure, in this instance, is to focus on the importance of the means to an end. Anyone may will a given end but a failure to will the appropriate means to reach that end prevents one from ever fulfilling one's aim. Again, the will discloses a disorder, but this time in regards to the full capacity of its willing power. These frailties and failures, which can beset the human will, reveal what transpires within the individual psychologically. Their presence is seen to produce an impact on the human being that will amount to a failure in the being, a kind of paralysis when it comes to willing what, normally speaking, one ought to will.

In yet another analysis of the evil in wrongful desire or of the disordered will, Augustine thinks of the problem in terms of being and God. Here the Scriptural sense of evil is seen to mesh with his philosophical analysis. He now recalls, first, the previous notion of plenitude as man's goal in existing and, second, that man is constituted to seek being and permanence with a capacity of will that allows him to act accordingly.

Now the apex of being and the good in the universe is God Himself. Thus, the more man approaches this end and becomes godlike, the more he achieves being and approaches the good, the good that is immutable, eternal and unable to be taken from man against his will. The more man, on the other hand, turns inward on himself or becomes attracted to beings beneath him the more he veers towards that which is mutable and able to be taken from him against his will.

This dual-directional motif deftly portrays the Scriptural notion that moral evil is a turning away from God, an aversion or defection, and that moral good is a turning towards God, a conversion that results in the good will or benevolent moral action. It is this broader Scriptural sense that comes to preoccupy Augustine later in life when he again reflects on the will, but then in regard to the issue of predestination and God's will.

What Augustine does think, however, at this point in his examination of human failure, is significant both for his basic position and subsequent exploration of the problem. Evil is the result of disorder in a being and, in the case of a rational and/or created intellectual being, a further disorder of its love. This disorder in love affects the will in such manner as to frustrate the tendency towards fulfilment in the being as such and to render the moral actions issuing from such a being deficient. Thus the will is not free by nature, that is, in its orientation towards good (God) for its completion in existence nor is it wholly free subsequently when affected by its failings, sin and evil. In the first case man's very satisfaction and fulfilment of being by communion with God means a built-in orientation for human nature's perfection, its plenitudo. In the latter condition the same nature is crippled and disoriented in making its decisions. Yet there always remains a freedom of decision in the directing of one's love. The same will, whether in a state of original nature or as fallen, always needs assistance from God to become a benevolent will but such assistance was and is always available to the will that decides to will, in accordance with its constituted nature.