Theories of morality are theories of right action — that is, theories about what makes an action right. The two major types of theories are consequentialist (or teleological) and formalist (or deontological). Consequentialist moral theories claim that the rightness of an action depends on its consequences. Act-utilitarianism is a consequentialist theory because right actions are supposed to result in more happiness than other possible actions. To put the point crudely, the basic idea behind such theories is that the end justifies the means.
Formalist moral theories claim that the rightness of an action depends on the action’s form. Here the consequences of an action don’t matter (or matter very little), but the form, or nature, of the action does. Such a theory might claim, for example, that killing an innocent person is always wrong because of the nature of that action, and this would be so whether or not the killing resulted in a great deal of good such as saving the lives of a hundred people. By this definition the Ten Commandments theory (TCT) is a formalist theory.
Consequentialist theories may be either religious or nonreligious. A religious person might say that an action is right if it results in the greatest amount of respect for sacred artifacts. A nonreligious person might claim that an action is right if it results in the greatest amount of pleasure for the greatest number of people. Formalist theories can also be religious or nonreligious.
Christian theories of ethics have traditionally been formalist, often maintaining that a certain kind of action is right or wrong no matter what the results. Nonreligious formalist theories are common too. Some of them claim, for example, that an action is right if it constitutes the performance of a certain duty, as in the ethical systems of the philosophers Immanuel Kant and W.D. Ross.
All humanist theories are nonreligious, and they too can be either consequentialist or formalist. Not all nonreligious theories, however, can be plausibly considered humanist. Humanism as a world view has traditionally incorporated a respect or concern for the welfare and the rights of human individuals. So utilitarianism earns the label of humanist because the crux of the theory is maximizing the happiness or pleasure of other human beings.
But the secular theory known as ethical egoism can’t plausibly be called humanist. It’s the view that right actions are those that promote one’s own self interest — a kind of moral self-absorption that is alien to humanist views of humanity. Ethical egoism also permits all manner of heinous acts as long as they are in the best interests of one’s self, acts that humanism would not condone.
Some moral theories are naturalistic and some nonnaturalistic, an important distinction that philosophers have debated for centuries. Naturalistic theories assert that morality can be derived from, or defined in terms of, natural phenomena. That is, people can know moral facts in the same way that a scientist can know physical or material facts. A naturalistic theory, for example, might maintain that ethical terms such as “morally right” can be equated with empirical phenomena like “producing more pleasure than pain.” Or a theory might say that being moral means meeting certain common human needs. Utilitarianism is a naturalistic moral theory.
Nonnaturalistic theories reject the idea that moral facts are somehow empirical facts. Proponents of these theories claim that moral terms cannot be reduced to empirical terms. The most famous nonnaturalistic slogan is that you “can’t get an ‘ought’ from an ‘is.'”
The idea that morality cannot be extracted from facts about the world was made most forcefully by the eighteenth-century philosopher David Hume — even though his own moral theory was naturalistic. The most famous nonnaturalistic moral theory is that of Immanuel Kant, who asserted that people have certain absolute moral duties that are derived not from empirical facts but from logical considerations. Some modern-day philosophers hold the nonnaturalistic (and nonreligious) view that there are universal moral principles that are logically self-evident.
Some people use the term “naturalistic” as a synonym for nonreligious. This way of using the word is perfectly acceptable, as long as the intended meaning is clear. We just need to keep in mind that in the field of ethics, most philosophers define “naturalistic” as we did above, using the term to emphasize the critical distinction between morality based on, and not based on, natural phenomena. (They may also sometimes use the term “naturalized” to mean much the same thing.) They would therefore want to say that religious moral theories can be naturalistic (empirical facts may define morality) or nonnaturalistic (morality comes from god) and that secular theories can also fall into either category. Note: Philosophers also apply “naturalistic” or “naturalized” to theories in epistemology (the study of knowledge) and to some areas of metaphysics (the study of the nature of reality), such as the mind-body problem and free will versus determinism.