With Volume III the theology Library moves into the area of 'moral theology'. Man and His Happiness studies moral matters in a comprehensive way in their general principles: voluntary acts and passions, virtues and vices, law and grace. Usually, moral theology is interested primarily in defining the moral issues of man's end, human acts, morality of human acts, and in subdividing the various contents of moral obligations and immoral situations. Moral theology as handled by the Theology Library is concerned with the implications of the Church's moral teaching in view of the modern problems and issues: the nature of a free act, the nature of law, of authority, in influence of grace in the human act, and then the positive development of human and supernatural virtues.