Philosophical theories of conscience might be categorized under three headings: moral knowledge theories, motivation theories, and reflection theories. People speak of their conscience “telling them to do” such-and-such. Such talk might imply that conscience is a source of moral knowledge about what to do. Moral knowledge theories of conscience try to explain how conscience affords us such knowledge. Some religious theories of conscience, for instance, interpret the voice of conscience as the voice of God within us. People also speak of “prickings” and “proddings” of conscience, or of their conscience urging them to do the right thing or bothering them if they have done (or are thinking of doing) the wrong thing. This suggests that conscience motivates us to do the right thing and to avoid the wrong thing. Conscience seems also to involve a certain way of thinking reflectively about what to do. This is usually a way of reflecting that gives first priority to moral considerations.

The three kinds of theory are not mutually exclusive. For example, Christian scholastic theories of conscience often distinguish synderesis (a notion derived from St. Jerome), which is a supposed source of moral knowledge, from conscience, which for some (e.g., St. Bonaventure) is an affective or volitional response to moral knowledge, while for others (e.g., St. Thomas Aquinas) it is the application of moral knowledge to action. St. Bonaventure's theory, therefore, combines knowledge and motivation.