Alex asked:

My question isn't really about philosophy, but about philosophers. Did A. J. Ayer and C. L. Stevenson
know each other? Did they ever spend time working together?

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Let me make a guess about where this question is coming from. In 1937, C.L. Stevenson wrote a
paper called 'The Emotive Meaning of Ethical Terms' in which he argued that ethical assertions are
not factual statements which can be true or false, but rather expressions of emotion. An expression of
emotion does not 'say' anything. Rather, it showsthat you have a certain attitude towards the thing
that prompts the expression of emotion, which can be favourable or unfavourable, for or against.

In his book Language, Truth and Logic, which was first published in 1936, A.J. Ayer proposed a very
similar, or identical account of the significance of ethical statements. Ayer argued that if ethical
statements were factual, then according to the verification principle, they must be capable, in
principle, of being verified by empirical investigation. But there is no way of empirically verifying
ethical statements. Therefore, ethical statements are not factual, but merely expressions of emotion.

Given the closeness in time, it is a matter of speculation which philosopher thought of the emotive
theory first. However, it wasn't necessary for them to have met or spent time working together, or
even influenced one another. Ayer's book brought the 'logical positivism' of Rudolph Carnap (Der
logische Aufbau der Welt1928, later translated as, The Logical Structure of The World) to the
attention of British philosophers — I am not so sure about the USA — and made a big impact when it
came out. The most likely explanation is that both philosophers were influenced by the prior writings
of Carnap.

Geoffrey Klempner