The Vienna Circle was an association
of philosophers who met to discuss the concept of logical positivism
(combination of empiricism and rationalism, also known as analytic
philosophy) as drawn from Ludwig Wittgenstein's Tractates
In Language, Truth, and Logic, Ayer put forth the central views of logical positivism which included the use of verifiability as a criterion of meaning. For example, a sentence is factually significant if, and only if, it is empirically verifiable to derive a number of conclusions, including the conclusions that (1) all metaphysical theories are meaningless, and (2) in describing things as being morally 'good' or 'bad', we are really just expressing our own attitudes
As an illustration, if we were to say that "killing is wrong", we would be attributing to acts of killing a certain moral property of it being wrong. According to Ayer, however, what we are really doing is expressing our attitude towards killing rather than a true or false claim about the act of killing itself.
It would be similar to saying "Hooray for the Yankees!" This sentence is not used to make any sort of claim, but is being used instead to express approval and support of a team. In Ayer's view the sentence, ‘Killing is wrong’, is used similarly to express our disapproval of killing rather than making a claim about the sentence being true or false.
While Ayer acknowledges that ethical terms can be included in factual statements, their inclusion adds nothing to its factual content: "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."
In Language, Truth and Logic, Ayer also rejected atheism in the same way he dismissed any religion - on the grounds that religious discourse is meaningless. He believed that religious language is unverifiable and, as such, nonsense. As a result, "There is no God" was for Ayer as meaningless and metaphysical a proclamation as "God exists."
Although Ayer himself was an atheist, he distinguished himself
from both agnostics and atheists by declaring that both of these
positions take the statement "God exists" as a meaningful
hypothesis, which Ayer does not.
In endorsing the views of logical positivism, Ayer saw himself as continuing in the tradition of British empiricism established by Locke, Hume and more recently Bertrand Russell. Throughout his career he continued to reject the possibility of an a priori knowledge. Instead, he saw the role of philosophy to be one of analyzing the meaning of such terms as 'causality', 'truth', 'knowledge', 'freedom' and the like. Thus the major portion of Ayer's work focused on exploring our claims to knowledge, particularly perceptual knowledge and knowledge that was dependant upon inductive reasoning for its credibility.
Amongst British philosophers of the 20th Century, Alfred, Jules Ayer has been ranked as second only to Bertrand Russell. In fact, some believe that his contribution to the theory of knowledge and general metaphysics is equal to that of Bertrand Russell.