Augustine and Sartre hailed from two different schools of thought, that of Christianity and that of Existentialism. Augustine's ideas of ethics are all based on the existence of a benevolent God. Augustine’s ethical theory follows the logic that God is good, and God created everything in our universe. Therefore, everything in our universe it good, albeit not necessarily “wholly” good. As a result, there are things that are not as good as others, and that is what we see as evil. Also central to Augustine’s ideology is the concept that God, out of his own morality, gives the individual the freedom to choose their actions. Thus, it follows that individuals are solely responsible for their own fortunes or misfortunes, punishments or rewards. Also part of Augustine’s ethical theory was his conviction that reason is inferior to divine knowledge, and thus without divine knowledge no amount of reason can lead to morality.
Sartre's ideas on the other hand, deny the existence of God. He argued that with the absence of God Sartre was an existentialist, and thus rejected any ideas of a universal principle that applies to all individuals. True to existentialist form. Sartre refused to look at the essence of humanity, instead favoring to look at the existence of humanity. Sartre's existentialism relates directly to the issue of ethics in that it holds the individual and only the individual responsible for his or her actions, be they ethical or unethical. For Satre, to claim that there are natural laws, or a universal principle, or an a priori set of guidelines that determine our actions is a delusional alleviation of our responsibilities. As far as Sartre is concerned, there is no such thing as a human nature, only a human condition. Sartre's idea that who we are is determined by the decision we make, not by some universal principle of human nature. Sartre holds the individual entirely responsible for his or her own actions. Not human nature, not social or natural order, nor the influence of others are responsible for our actions.
Augustine and Sartre both hold the individual responsible for their actions, even if for different reasons. Augustine holds the individual responsible because he believes that God has given the individual the choice between good and evil. Sartre, who denies God, holds the individual responsible for that reason. If there is no God, then there is no universal principle that governs our lives, we choose our actions and our decisions. Both philosophers agree that the individual makes the decisions, and it is the individual who is accountable for those decisions.