Metaethics

Cognitivist theories hold that evaluative moral sentences express propositions (i.e., they are 'truth-apt' or 'truth bearers', capable of being true or false), as opposed to non-cognitivism. Most forms of cognitivism hold that some such propositions are true (including moral realism and ethical subjectivism), as opposed to error theory, which asserts that all are erroneous.

Moral realism (in the robust sense; see moral universalism for the minimalist sense) holds that such propositions are about robust or mind-independent facts, that is, not facts about any person or group's subjective opinion, but about objective features of the world. Metaethical theories are commonly categorized as either a form of realism or as one of three forms of "anti-realism" regarding moral facts: ethical subjectivism, error theory, or non-cognitivism. Realism comes in two main varieties:

1. Ethical naturalism holds that there are objective moral properties and that these properties are reducible or stand in some metaphysical relation (such as supervenience) to entirely non-ethical properties. Most ethical naturalists hold that we have empirical knowledge of moral truths. Ethical naturalism was implicitly assumed by many modern ethical theorists, particularly utilitarians.
2. Ethical non-naturalism, as put forward by G. E. Moore, holds that there are objective and irreducible moral properties (such as the property of 'goodness'), and that we sometimes have intuitive or otherwise a priori awareness of moral properties or of moral truths. Moore's open question argument against what he considered the naturalistic fallacy was largely responsible for the birth of metaethical research in contemporary analytic philosophy.

Ethical subjectivism is one form of moral anti-realism. It holds that moral statements are made true or false by the attitudes and/or conventions of people, either those of each society, those of each individual, or those of some particular individual. Most forms of ethical subjectivism are relativist, but there are notable forms that are universalist:

• Ideal observer theory holds that what is right is determined by the attitudes that a hypothetical ideal observer would have. An ideal observer is usually characterized as a being who is perfectly rational, imaginative, and informed, among other things. Though a subjectivist theory due to its reference to a particular (albeit hypothetical) subject, Ideal Observer Theory still purports to provide universal answers to moral questions.
• Divine command theory holds that for a thing to be right is for a unique being, God, to approve of it, and that what is right for non-God beings is obedience to the divine will. This view was criticized by Plato in the Euthyphro (see the Euthyphro problem) but retains some modern defenders (Robert Adams, Philip Quinn, and others). Like ideal observer theory, divine command theory purports to be universalist despite its subjectivism.

Error theory, another form of moral anti-realism, holds that although ethical claims do express propositions, all such propositions are false. Thus, both the statement "Murder is morally wrong" and the statement "Murder is morally permissible" are false, according to error theory. J. L. Mackie is probably the best-known proponent of this view. Since error theory denies that there are moral truths, error theory entails moral nihilism and, thus, moral skepticism; however, neither moral nihilism nor moral skepticism conversely entail error theory.

Non-cognitivist theories hold that ethical sentences are neither true nor false because they do not express genuine propositions. Non-cognitivism is another form of moral anti-realism. Most forms of non-cognitivism are also forms of expressivism, however some such as Mark Timmons and Terrence Horgan distinguish the two and allow the possibility of cognitivist forms of expressivism. Non-cognitivism includes:

• Emotivism, defended by A. J. Ayer and Charles Stevenson, holds that ethical sentences serve merely to express emotions. Ayer argues that ethical sentences are expressions of approval or disapproval, not assertions. So "Killing is wrong" means something like "Boo on killing!".
• Quasi-realism, defended by Simon Blackburn, holds that ethical statements behave linguistically like factual claims and can be appropriately called "true" or "false", even though there are no ethical facts for them to correspond to. Projectivism and moral fictionalism are related theories.
• Universal prescriptivism, defended by R. M. Hare, holds that moral statements function like universalized imperative sentences. So "Killing is wrong" means something like "Don't kill!" Hare's version of prescriptivism requires that moral prescriptions be universalizable, and hence actually have objective values, in spite of failing to be indicative statements with truth-values per se.

Yet another way of categorizing metaethical theories is to distinguish between centralist and non-centralist moral theories. The debate between centralism and non-centralism revolves around the relationship between the so-called "thin" and "thick" concepts of morality: thin moral concepts are those such as good, bad, right, and wrong; thick moral concepts are those such as courageous, inequitable, just, or dishonest.[2] While both sides agree that the thin concepts are more general and the thick more specific, centralists hold that the thin concepts are antecedent to the thick ones and that the latter are therefore dependent on the former. That is, centralists argue that one must understand words like "right" and "ought" before understanding words like "just" and "unkind." Non-centralism rejects this view, holding that thin and thick concepts are on par with one another and even that the thick concepts are a sufficient starting point for understanding the thin ones.[3][4]

Non-centralism has been of particular importance to ethical naturalists in the late 20th and early 21st centuries as part of their argument that normativity is a non-excisable aspect of language and that there is no way of analyzing thick moral concepts into a purely descriptive element attached to a thin moral evaluation, thus undermining any fundamental division between facts and norms. Allan Gibbard, R. M. Hare, and Simon Blackburn have argued in favor of the fact/norm distinction, meanwhile, with Gibbard going so far as to argue that, even if conventional English has only mixed normative terms (that is, terms that are neither purely descriptive nor purely normative), we could develop a nominally English metalanguage that still allowed us to maintain the division between factual descriptions and normative evaluations.[5][6]

Moral universalism (or universal morality) is the metaethical position that some system of ethics, or a universal ethic, applies universally, that is to all intelligent beings regardless of culture, race, sex, religion, nationality, sexuality, or other distinguishing feature. The source or justification of this system may be thought to be, for instance, human nature, shared vulnerability to suffering, the demands of universal reason, what is common among existing moral codes, or the common mandates of religion (although it can be argued that the latter is not in fact moral universalism because it may distinguish between Gods and mortals). Moral universalism is the opposing position to various forms of moral relativism.

Universalist theories are generally forms of moral realism, though exceptions exists, such as the subjectivist ideal observer and divine command theories, and the non-cognitivist universal prescriptivism of R. M. Hare. Forms of moral universalism include:

• Value monism is the common form of universalism, which holds that all goods are commensurable on a single value scale.
• Value pluralism contends that there are two or more genuine scales of value, knowable as such, yet incommensurable, so that any prioritization of these values is either non-cognitive or subjective. A value pluralist might, for example, contend that both a life as a nun and a life as a mother realize genuine values (in a universalist sense), yet they are incompatible (nuns may not have children), and there is no purely rational way to measure which is preferable. A notable proponent of this view is Isaiah Berlin.

Moral relativism maintains that all moral judgments have their origins either in societal or in individual standards, and that no single standard exists by which one can objectively assess the truth of a moral proposition. Metaethical relativists, in general, believe that the descriptive properties of terms such as "good", "bad", "right", and "wrong" do not stand subject to universal truth conditions, but only to societal convention and personal preference. Given the same set of verifiable facts, some societies or individuals will have a fundamental disagreement about what one ought to do based on societal or individual norms, and one cannot adjudicate these using some independent standard of evaluation. The latter standard will always be societal or personal and not universal, unlike, for example, the scientific standards for assessing temperature or for determining mathematical truths. Some philosophers maintain that moral relativism entails non-cognitivism, while others consider it a form of cognitivism. Some but not all relativist theories are forms of moral subjectivism, although not all subjectivist theories are relativistic.

Moral nihilism, also known as ethical nihilism, is the metaethical view that nothing has intrinsic moral value. For example, a moral nihilist would say that killing someone, for whatever reason, is intrinsically neither morally right nor morally wrong. Moral nihilism must be distinguished from moral relativism, which does allow for moral statements to be intrinsically true or false in a non-universal sense, but does not assign any static truth-values to moral statements. Insofar as only true statements can be known, moral nihilists are moral skeptics. Most forms of moral nihilism are non-cognitivist and vice versa, though there are notable exceptions such as universal prescriptivism (which is semantically non-cognitive but substantially universal).

Empiricism is the doctrine that knowledge is gained primarily through observation and experience. Metaethical theories that imply an empirical epistemology include:

• ethical naturalism, which holds moral facts to be reducible to non-moral facts and thus knowable in the same ways; and
• most common forms of ethical subjectivism, which hold that moral facts reduce to facts about individual opinions or cultural conventions and thus are knowable by observation of those conventions.

There are exceptions within subjectivism however, such as ideal observer theory, which implies that moral facts may be known through a rational process, and individualist ethical subjectivism, which holds that moral facts are merely personal opinions and so may be known only through introspection. Empirical arguments for ethics run into the is-ought problem, which asserts that the way the world is cannot alone instruct people how they ought to act.

Moral rationalism, also called ethical rationalism, is the view according to which moral truths (or at least general moral principles) are knowable a priori, by reason alone. Plato and Immanuel Kant, prominent figures in the history of philosophy, defended moral rationalism. David Hume and Friedrich Nietzsche are two figures in the history of philosophy who have rejected moral rationalism.

Recent philosophers who defended moral rationalism include R. M. Hare, Christine Korsgaard, Alan Gewirth, and Michael Smith. A moral rationalist may adhere to any number of different semantic theories as well; moral realism is compatible with rationalism, and the subjectivist ideal observer theory and non-cognitivist universal prescriptivism both entail it.

Ethical intuitionism is the view according to which some moral truths can be known without inference. That is, the view is at its core a foundationalism about moral beliefs. Such an epistemological view implies that there are moral beliefs with propositional contents; so it implies cognitivism. Ethical intuitionism commonly suggests moral realism, the view that there are objective facts of morality and, to be more specific, ethical non-naturalism, the view that these evaluative facts cannot be reduced to natural fact. However, neither moral realism nor ethical non-naturalism are essential to the view; most ethical intuitionists simply happen to hold those views as well. Ethical intuitionism comes in both a "rationalist" variety, and a more "empiricist" variety known as moral sense theory.

Moral skepticism is the class of metaethical theories all members of which entail that no one has any moral knowledge. Many moral skeptics also make the stronger, modal, claim that moral knowledge is impossible. Forms of moral skepticism include, but are not limited to, error theory and most but not all forms of non-cognitivism.