One attribute of any ethical code is whether it relies on an internal or external moral code. For instance, both Subjectivist and Egoist ethics rely on internal ethical codes- the judgement of one's conduct is based on either one's emotional response to an action or whether that action promotes one's own well-being. On the other hand, there are codes that rely on an external source of morality, whether it be God's commands, or an inherent morality within nature, or some such source. Examples of this type of ethics would include Divine Command Theory and Natural Law Theory.

Within the group of ethical theories mentioned above, the most reasonable is Natural Law theory. Natural Law theory, the idea that God has created everything in the universe with a purpose defined in a "universal law" from which the "natural laws" descend, describing the behavior of the universe and the objects therein. Man's share in this law, argues St. Thomas Aquinas, as related by James Rachels in The Elements of Moral Philosophy, is the ability to reason, by which we should find the natural laws, and extend these natural laws to include our own ethical and moral laws. The end result is that the ethical principles by which we should live are determined by reason as a reflection of the objective moral law God has set upon the universe. However, Natural Law theory does suffer from the problem that it makes a logical leap from what is, in the form of the natural or universal law or laws within the universe, to what should be, in the form of man's moral and ethical codes, as an unsupported act of reason, without providing for a value judgement or an additional premise indicating why this is an acceptable conclusion.

The other theories mentioned are all less believable. Subjectivism is the idea that and individual's opinion on the rightness or wrongness of an action originates with how an individual feels about the action. However, this theory provides no means for ascertaining whether that individual is reasonably correct in their feelings, and it makes conflicts irresolvable unless there is a means of deciding whether one individual's feelings are better than another’s, or more 'valid' than another's. This would seem to render the theory relatively unacceptable.

Divine command theory, which holds that ethical acts coincide with God's commands relating to the issue, is at first blush and extremely simple and attractive theory. However, when the question is posed, as it was by Socrates, of whether an action is right because God commanded it or if God commanded it because it is right, the theory begins to have problems. Socrates' dilemma has a difficult conclusion on either choice, either making God arbitrary and not worthy of praise, or making Him irrelevant.