 Premise 4 is the key addition. It is not the only way to arrive at a broadly expressivist theory in ethics – earlier forms, such as emotivism (Ayer 1936; Stevenson 1944) and universal prescriptivism (Hare 1952) relied on the problematic assumption that the meaning of a sentence is to be understood on the basis of the effects it is used to achieve or the speech act it is used to perform. Metasemantic Psychologism doesn’t make this assumption, but simply derives the meaning of linguistic expressions from the thoughts that they express, rather than their truth-conditions or the possible worlds they rule out, as standard semantics does (Gibbard 1990: 92)