“The presence of an ethical symbol in a proposition adds nothing to its factual content. Thus if I say to someone, ‘You acted wrongly in stealing that money’, I am not stating anything more than if I had simply said, ‘You stole that money’. In adding that this action is wrong I am not making any further statement about it. I am simply evincing my moral disapproval of it. It is as if I had said, ‘You stole that money’ in a peculiar tone of horror, or written it with the addition of some special exclamation marks. The tone, or the exclamation marks, adds nothing to the literal meaning of the sentence. It merely serves to show that theexpression of it is attended by certain feelings in the speaker” (A.J. Ayer LTL., p. 107)

So in Ayer’s view, ‘stealing is wrong’ is a sentence without factual meaning, and he glosses this claim with the remark that such a sentence ‘expresses no proposition which can be either true or false’.

It follows from this position that disagreement about whether stealing is wrong arises merely out of different feelings about stealing. And it follows from this that if I disagree with you when you say that stealing is wrong, I do not thereby contradict you. The thought here is that I only contradict you in the case where I deny that what you say is true (or false). And in the present case questions of truth and falsehood simply don’t arise.

When I use ethical terms I am merely ’emoting’. I am not making an assertion that could be true or false. I am expressing an attitude (e.g., a ‘pro-attitude’, or a ‘con-attitude’.) But it is important to recognise that the doctrine is not restricted to saying that I am expressing an emotion or an attitude. Ethical terms are ‘calculated also to arouse feeling, and so to stimulate action’.

To read Ayer for yourself, chapter 6 is here.