1936/Ayer

==Ideas==
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* It was crucial in bringing some of the ideas of the Vienna Circle and the logical empiricists to the attention of the English-speaking world.
* This book defines, explains, and argues for the verification principle of logical positivism, sometimes referred to as the "criterion of significance" or "criterion of meaning". It explains how the principle of verifiability may be applied to the problems of philosophy.
* According to Ayer, analytic statements are tautologies. A tautology is a statement that is necessarily true, true by definition, and true under any conditions. A tautology is a repetition of the meaning of a statement, using different words or symbols. According to Ayer, the statements of logic and mathematics are tautologies. Tautologies are true by definition, and thus their validity does not depend on empirical testing.
* Every verifiable proposition is meaningful, although it may be either true or false. Every proposition asserts or denies something, and thus is either true or false.
* Literal meaning must ... be distinguished from factual meaning. Literal meaning is an attribute of statements that are either analytic or empirically verifiable. Factual meaning is an attribute of statements that are meaningful without being analytic. Thus, statements that have factual meaning say something about the real world.
* Ayer agrees with Hume that there are two main classes of propositions: those that concern 'relations of ideas,' and those that concern 'matters of fact.' Propositions about 'relations of ideas' include the a priori propositions of logic and mathematics. Propositions about 'matters of fact,' on the other hand, make assertions about the empirical world.
* Ayer argues that philosophic propositions are analytic, and that they are concerned with 'relations of ideas.' The task of philosophy is to clarify the logical relationships of empirical propositions. If the meaning of propositions is defined by verifiability, then philosophy cannot provide speculative truths about metaphysical statements that cannot be empirically verified.
* Ayer rejects the metaphysical thesis that philosophy can give us knowledge of a transcendent reality. He dismisses metaphysical arguments, calling them nonsense, and saying that they cannot be empirically verified. He argues that metaphysical statements have no literal meaning, and that they cannot be subjected to criteria of truth or falsehood.
* A significant consequence of abandoning metaphysics as a concern of philosophy is a rejection of the view that the function of philosophy is to propose basic principles of meaning and to construct a deductive system by offering the consequences of these principles of meaning as a complete picture of reality. But this is, some may argue, what Ayer does, in presenting the principle of verifiability as a criterion of meaningfulness for any empirical proposition.
* In Ayer's logical empiricism, philosophy is no longer seen as a metaphysical concern, nor as an attempt to provide speculative truths about the nature of ultimate reality. Instead, philosophy is seen as an activity of defining and clarifying the logical relationships of empirical propositions. In considering how to distinguish between a conscious man and an unconscious machine,p. 140. Penguin, 2001. Ayer also anticipates the development in 1950 of the Turing test to test a machine's capability to demonstrate intelligence (consciousness).
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