Consequentialism is the view that the only morally relevant feature (aspect, property, characteristic, attribute) of an action is its consequences. That is to say, in determining whether an action is right or wrong, only one thing matters: its consequences. Motives don’t matter; the type of action it is (e.g., a lie, a killing of an innocent person, a broken promise) doesn’t matter; whether the action can be universalized doesn’t matter.
As for which consequences matter, that depends on the theory. Here is an egoistic version of consequentialism: An action is right if and only if it has the best consequences for the agent (the one performing the action). Most consequentialists are universalists or impartialists rather than particularists or partialists. (Egoism is one type—an extreme type—of partialism. Others are familialism, tribalism, racialism, nationalism, and humanism.) They say that everyone affected by the action, and not just the agent, matters.
Another distinction is between act-consequentialism and rule-consequentialism. The act-consequentialist evaluates actions directly. The rule-consequentialist evaluates actions indirectly, by asking whether they fall under a rule which, if generally followed, would have the best overall consequences. For example, the rule that one ought not to lie has better overall consequences (arguably) than a rule that allows lying at whim; so, even if a particular lie would have the best overall consequences, it would be wrong to lie. Both types of consequentialism evaluate actions as right or wrong, and both do so solely in terms of consequences. They differ in whether the evaluation is direct (immediate) or indirect (mediate).
Consequentialism requires a theory of the good. It must specify which states of affairs are good, for it requires that agents bring about as much good as they can at any given time. Some consequentialists are hedonists. They seek to maximize the amount of pleasure (or happiness) in the world. Others are welfarists. They seek to maximize overall welfare (well-being), even if it doesn’t increase pleasure or happiness. Consequentialism is a maximizing theory. If there are two actions available to me and one of them produces only slightly more good than the other, I am obligated to perform the action that produces slightly more good. If I perform the other action, I act wrongly. Consequentialism makes the good logically prior to the right. The right, in other words, is defined in terms of the good. To act rightly, one must bring about as much good as one can.
The word “deontology” (literally, study or science of [logos] duty [deon]) is used in different senses. Some philosophers use it to mean nonconsequentialism, which has the advantage of cleanly partitioning the class of normative ethical theories. In this way of thinking, any theory that denies the central claim of consequentialism—viz., that the only morally relevant feature of an action is its consequences—would count as deontological. Note that deontology, so understood, does not deny the moral relevance of consequences. It says that consequences aren’t everything. Something else, such as the motive with which the action is performed, also counts. Consequentialism, theoretically speaking, is pure and simple; deontology is impure and complicated. Of course, purity and simplicity don’t make a theory correct. If the moral life is complicated, then perhaps our theory of rightness should be complicated. Consequentialism may be simplistic as well as simple.
Consequentialism has been assailed as both too permissive and too demanding. It’s arguably too permissive because it allows individuals to harm others in pursuit of the greatest good. If my killing you (an innocent person) is the only way to save ten other innocent persons, then it’s right for me to kill you. It’s arguably too demanding because it requires individuals to work full time to alleviate misery. Consequentialism (I speak here of impartial consequentialism, the most common type) makes no distinction between self, family members, friends, colleagues, compatriots, and strangers. Everyone counts equally. My own interests count for no more (or less) than those of anyone else, including people in faraway lands whose lives, customs, and religious beliefs are very different from mine. Peter Singer, the author of “Famine, Affluence, and Morality,” is a consequentialist. You can see why he believes that each of us has a moral duty to relieve and prevent famine. It’s not merely a good thing that we do this, he says; it’s required. We act wrongly if we live comfortable lives while others are suffering.
To a consequentialist, that an action is of a particular type—say, a lie, a broken promise, a killing of an innocent person, a torture—is morally irrelevant. Of course, a rule-consequentialist can say that the rule against torture, if generally followed, would maximize the overall good, and that individual acts of torture are therefore wrong. But torture, in this view, is not wrong because it’s torture; it’s wrong because it’s the sort of act that tends to produce bad consequences. Put differently, the wrongness of torture is extrinsic to it, not intrinsic to it.
Things are otherwise for the deontologist. The deontologist holds that certain actions are intrinsically wrong. They are wrong not because of their consequences or any other extrinsic feature, but because of the kinds of actions they are. This doesn’t mean that deontologists are absolutists. Some are; some are not. An absolutist deontologist holds that certain actions, such as torture, must not be performed no matter how good the consequences of doing so. A moderate (i.e., nonabsolutist) deontologist holds that certain actions, such as torture, are intrinsically wrong, but may be performed if enough good would be produced thereby. I said that consequentialists make the good logically prior to the right. Deontologists make the right logically prior to the good. Do you see the difference?
Please don’t conflate moderate deontology and consequentialism. They’re different. That neither is absolute doesn’t make them the same theory. Here’s a summary of the three theories (or theory-types):
• Consequentialism: No act-type is intrinsically wrong. Rightness and wrongness are extrinsic properties of actions.It’s unfortunate, but some consequentialists dismiss deontology on grounds that it’s absolute. They set up a false dichotomy: Either you’re a consequentialist or you’re an absolutist deontologist. Since many people resist absolutism, they think they’re committed to consequentialism. Not so. Moderate deontology is a viable alternative.
• Moderate deontology: Some act-types are intrinsically wrong, but may be performed if enough good would be brought about.
• Absolutist deontology: Some act-types are intrinsically wrong and may not be performed no matter how much good would be brought about.
In case you’re wondering, many prominent philosophers are deontologists. Here is a partial list: John Rawls, Thomas Nagel, Immanuel Kant, Robert Nozick, Ronald Dworkin, Charles Fried, G. E. M. Anscombe, Bernard Williams, John Finnis, Alan Donagan, Joel Feinberg, Bernard Gert, Judith Jarvis Thomson, Samuel Scheffler, and T. M. Scanlon. There are many prominent consequentialists as well, such as Jeremy Bentham, John Stuart Mill, Henry Sidgwick, J. J. C. Smart, R. M. Hare, Richard B. Brandt, L. W. Sumner, Peter Singer, and Shelly Kagan. The debate between consequentialism and deontology is alive and well, as I suspect it always will be. Don’t say that they should compromise. Given how the theories are defined, no compromise is possible. Either you believe that only consequences matter or you believe that something besides consequences matters. This is an unbridgeable, permanent divide in ethical theory.
I hope this helps. If you have questions, write to me. If you want to read more about normative ethical theory, please acquire and read Shelly Kagan’s Normative Ethics (Boulder, CO: Westview Press, 1998). Some of the distinctions I make in this post derive from this book, which is one of the best books I’ve read—on any topic.