A. J. Ayer
Sir Alfred Jules Ayer (1910-) - author of Language, Truth and Logic (1936) in
which he argues, in part, that normative sentences are literally nonsense; they
are not empirically verifiable and therefore contain no propositional content.
This does not mean, however, that normative sentences are useless. On the
contrary, Ayer argued normative sentences were 'emotive', either demonstrating
the emotions of the speaker or stirring the emotions of the listener.
Read more about A.J. Ayer.
See also the Stanford Encyclopedia of Philosophy on Ayer.