Note: the following has been abstracted from the Grolier Encyclopedia.
Logical positivism, also known as logical empiricism, scientific empiricism, and consistent empiricism, is a school of philosophy founded in Vienna during the 1920s by a group of scientists, mathematicians, and philosophers known as the Vienna Circle. Among its most prominent members were Moritz Schlick, the leader of the group; Rudolf Carnap; and Kurt Godel. They derived much of their inspiration from the writings of Ernst Mach, Gottlob Frege, Bertrand Russell, Ludwig Wittgenstein, and George Edward Moore.
Members of the group shared a distaste for metaphysical speculation. They considered the assertions of traditional metaphysics as meaningless, because it was impossible to verify them in experience. In their view, if a metaphysician makes the claim "Reality is the Absolute," it is a waste of time to argue the point, for no possible experience is relevant to ascertaining whether or not such a claim is true. According to their reasoning, it would be equally senseless to advocate that "Reality is not the Absolute," for this claim cannot be verified either. Hence all such assertions, and all disputes about them, are meaningless.
The main theses of logical positivism were presented in many articles and books. They were given prominence, however, through Sir Alfred Ayer's Language, Truth, and Logic, first published in 1936. These tenets, some of which were subsequently modified and refined by other logical positivists, may be briefly stated as follows: (1) A proposition, or a statement, is factually meaningful only if it is verifiable. This is understood in the sense that the proposition can be judged probable from experience, not in the sense that its truth can be conclusively established by experience. (2) A proposition is verifiable only if it is either an experiential proposition or one from which some experiential proposition can be deduced in conjunction with other premises. (3) A proposition is formally meaningful only if it is true by virtue of the definitions of its terms--that is, tautologous. (4) The laws of logic and mathematics are all tautologous. (5) A proposition is literally meaningful only if it is either verifiable or tautologous. (6) Since metaphysical statements are neither verifiable nor tautologous, they are literally meaningless. (7) Since ethical, aesthetical, and theological statements also fail to meet the same conditions, they too are cognitively meaningless--although they may possess "emotive" meaning. (8) Since metaphysics, ethics, philosophy of religion, and aesthetics are all eliminated, the only tasks of philosophy are clarification and analysis. Thus, the propositions of philosophy are linguistic, not factual, and philosophy is a department of logic.
After the Nazis took control of Austria in 1938, the Vienna Circle broke up, and logical positivism, as a movement, came to an end. The work of the logical positivists, however, continues in the modern emphasis on the analysis of language as a function of philosophy.