This makes emotivism a form of non-cognitivism or expressivism. Emotivism stands in opposition to other forms of non-cognitivism (such as quasi-realism and universal prescriptivism), as well as to all forms of cognitivism (including both objectivist theories such as moral realism, and subjectivist theories such as moral relativism).
Influenced by the growth of analytic philosophy and logical positivism in the 20th century, the theory was stated most vividly by A. J. Ayer in his 1936 book Language, Truth and Logic, but its development owes even more to C. L. Stevenson. In the 1950s, emotivism appeared in a modified form in the universal prescriptivism of R. M. Hare.
Emotivism reached prominence in the 20th century, but it was born centuries earlier. In 1710, George Berkeley wrote that language in general often serves to inspire feelings as well as communicate ideas. Decades later, David Hume espoused ideas similar to Stevenson's later ones. In his 1751 book An Enquiry Concerning the Principles of Morals, Hume considered morality to be related to fact but "determined by sentiment":
G. E. Moore published his Principia Ethica in 1903 and argued that the attempts of ethical naturalists to translate ethical terms (like good and bad) into non-ethical ones (like pleasing and displeasing) committed the "naturalistic fallacy". Moore was a cognitivist, but his case against ethical naturalism steered other philosophers toward noncognitivism, particularly emotivism.
The emergence of logical positivism and its verifiability criterion of meaning early in the 20th century led some philosophers to conclude that ethical statements, being incapable of empirical verification, were cognitively meaningless. This criterion was fundamental to Ayer's defense of positivism in Language, Truth and Logic, which contains his statement of emotivism. However, positivism is not essential to emotivism itself, perhaps not even in Ayer's form, and some positivists in the Vienna Circle, which had great influence on Ayer, held non-emotivist views.
R. M. Hare unfolded his ethical theory of universal prescriptivism in 1952's The Language of Morals, intending to defend the importance of rational moral argumentation against the "propaganda" he saw encouraged by Stevenson, who thought moral argumentation was sometimes psychological and not rational. But Hare's disagreement was not universal, and the similarities between his noncognitive theory and the emotive one — especially his claim, and Stevenson's, that moral judgments contain commands and are thus not purely descriptive — caused some to regard him as an emotivist, a classification he denied:
He focuses on propositions of the first class—moral judgments—saying that those of the second class belong to science, those of the third are mere commands, and those of the fourth (which are considered in normative ethics as opposed to meta-ethics) are too concrete for ethical philosophy. While class three statements were irrelevant to Ayer's brand of emotivism, they would later play a significant role in Stevenson's.
Ayer argues that moral judgments cannot be translated into non-ethical, empirical terms and thus cannot be verified; in this he agrees with ethical intuitionists. But he differs from intuitionists by discarding appeals to intuition as "worthless" for determining moral truths, since the intuition of one person often contradicts that of another. Instead, Ayer concludes that ethical concepts are "mere pseudo-concepts":
Ayer agrees with subjectivists in saying that ethical statements are necessarily related to individual attitudes, but he says they lack truth value because they cannot be properly understood as propositions about those attitudes; Ayer thinks ethical sentences are expressions, not assertions, of approval. While an assertion of approval may always be accompanied by an expression of approval, expressions can be made without making assertions; Ayer's example is boredom, which can be expressed through the stated assertion "I am bored" or through non-assertions including tone of voice, body language, and various other verbal statements. He sees ethical statements as expressions of the latter sort, so the phrase "Theft is wrong" is a non-propositional sentence which is an expression of disapproval but is not equivalent to the proposition "I disapprove of theft".
Having argued that his theory of ethics is noncognitive and not subjective, he accepts that his position and subjectivism are equally confronted by G. E. Moore's argument that ethical disputes are clearly genuine disputes and not just expressions of contrary feelings. Ayer's defense is that all ethical disputes are about facts regarding the proper application of a value system to a specific case, not about the value systems themselves, because any dispute about values can only be resolved by judging that one value system is superior to another, and this judgment itself presupposes a value system. If Moore is wrong in saying that there are actual disagreements of value, we are left with the claim that there are actual disagreements of fact, and Ayer accepts this without hesitation:
Imperatives cannot be proved, but they can still be supported so that the listener understands that they are not wholly arbitrary:
The purpose of these supports is to make the listener understand the consequences of the action they are being commanded to do. Once they understand the command's consequences, they can determine whether or not obedience to the command will have desirable results.
In second-pattern analysis, rather than judge an action directly, the speaker is evaluating it according to a general principle. For instance, someone who says "Murder is wrong" might mean "Murder decreases happiness overall"; this is a second-pattern statement which leads to a first-pattern one: "I disapprove of anything which decreases happiness overall. Do so as well.
Logical methods involve efforts to show inconsistencies between a person's fundamental attitudes and their particular moral beliefs. For example, someone who says "Edward is a good person" who has previously said "Edward is a thief" and "No thieves are good people" is guilty of inconsistency until she retracts one of her statements. Similarly, a person who says "Lying is always wrong" might consider lies in some situations to be morally permissible, and if examples of these situations can be given, his view can be shown to be logically inconsistent.
Rational psychological methods examine the facts which relate fundamental attitudes to particular moral beliefs; the goal is not to show that someone has been inconsistent, as with logical methods, but only that they are wrong about the facts which connect their attitudes to their beliefs. To modify the former example, consider the person who holds that all thieves are bad people. If she sees Edward pocket a wallet found in a public place, she may conclude that he is a thief, and there would be no inconsistency between her attitude (that thieves are bad people) and her belief (that Edward is a bad person because he is a thief). However, it may be that Edward recognized the wallet as belonging to a friend, to whom he promptly returned it. Such a revelation would likely change the observer's belief about Edward, and even if it did not, the attempt to reveal such facts would count as a rational psychological form of moral argumentation.
Non-rational psychological methods revolve around language with psychological influence but no necessarily logical connection to the listener's attitudes. Stevenson called the primary such method "'persuasive,' in a somewhat broadened sense", and wrote:
Persuasion may involve the use of particular emotion-laden words, like "democracy" or "dictator", or hypothetical questions like "What if everyone thought the way you do?" or "How would you feel if you were in their shoes?
James Urmson's 1968 book The Emotive Theory of Ethics also disagreed with many of Stevenson's points in Ethics and Language, "a work of great value" with "a few serious mistakes [which] led Stevenson consistently to distort his otherwise valuable insights".
It would make little sense to translate a statement such as "Galileo should not have been forced to recant on heliocentricism" into a command, imperative, or recommendation. In fact, it is not clear how such a task would even be possible without radically changing the meaning of these ethical statements. Under this criticism, it would appear as if emotivist and prescriptivist theories are only capable of converting a relatively small subset of all ethical claims into imperatives.
Like Ross and Brandt, Urmson disagrees with Stevenson's "causal theory" of emotive meaning — the theory that moral statements only have emotive meaning when they are made in order to cause a change in a listener's attitude — saying that is incorrect in explaining "evaluative force in purely causal terms". This is Urmson's fundamental criticism, and he suggests that Stevenson would have made a stronger case by explaining emotive meaning in terms of "commending and recommending attitudes", not in terms of "the power to evoke attitudes".
Stevenson's Ethics and Language, written after Ross's book but before Brandt's and Urmson's, states that emotive terms are "not always used for purposes of exhortation." For example, in the sentence "Slavery was good in Ancient Rome", Stevenson thinks one is speaking of past attitudes in an "almost purely descriptive" sense. And in some discussions of current attitudes, "agreement in attitude can be taken for granted," so a judgment like "He was wrong to kill them" might describe one's attitudes yet be "emotively inactive", with no real emotive (or imperative) meaning. Stevenson is doubtful that sentences in such contexts qualify as normative ethical sentences, maintaining that "for the contexts that are most typical of normative ethics, the ethical terms have a function that is both emotive and descriptive."