Like G. E. Moore and Charles Sanders Peirce, A. J. Ayer wanted to identify the kinds of propositions suitable for logical analysis. He argued that only two types are meaningful: those that are empirically verifiable and those that are analytic. Propositions of the first type are classified as factual, those of the second are called relations of ideas and are represented by logic and mathematics. Ayer, agreeing with Peirce, emphasized that all empirical statements are provisional, that they can always be invalidated by future events. On the other hand, metaphysical statements–particularly those of religion--were unfalsifiable and therefore “nonsensical”; a similar claim was made for ethics and aesthetics. Although the truth value of metaphysical, ethical, and aesthetic statements could not be established, they did have emotive value, resulting in a clearer understanding of individual and group psychology.
Ayer’s beliefs were strongly influenced by the Vienna Circle, a philosophic group that met during the 1920s and 1930s to promote Logical Positivism. Its members included Rudolf Carnap, Moritz Schlick (the leader), Hans Hahn, and Otto Neurath. Wittgenstein’s Tractatus was the key inspiration for the group’s formation; ironically he did not consider himself a logical positivist or a member of the Circle, but he attended some of its meetings and corresponded actively with participants.
Language, Truth and Logic is about 150 pages and available from amazon.com ($6.95 new and from $0.01 used). Ayer targeted the book to the non-specialist, hence the writing is easily understandable (at least compared to other philosophers we have read) and without much jargon or symbolic notations. A free public domain copy can be downloaded here.
The following resources provide commentary, bibliographies, lecture notes, and videos.
Wikipedia: "A. J. Ayer", "Language, Truth and Logic", "Logical Positivism", "Vienna Circle"
Stanford Encyclopedia of Philosophy: "Alfred Jules Ayer", "Logical Empiricism", "Vienna Circle"
The Cambridge Companion to Logical Empiricism. Ed. Alan Richardson and Thomas Uebel. Cambridge University Press, 2007. This is the complete 417 page text; of particular value is Friedrich Stadler's "The Vienna Circle: Context, Profile, and Development"
"Logical Positivism" (web site of Mauro Murzi; useful brief articles on various aspects of the subject)
Ted Honderich, "A. J. Ayer's Philosophy and Its Greatness", Professor Emeritus of the Philosophy of Mind, University College London
Bertrand Russell, "Review of Language,Truth and Logic, 2nd edition (1947)" Horizon 15 (Janaury 1947): 71-72.
Pierre Cruse, “Language Truth and Logic” Richmond Journal of Philosophy 6 (Spring 2004): 1-12 (detailed analysis of the verification principle)
Michael Lacewing, “Religious Language and Verificationism” Routledge Philosophy A Level Web Site
Geoffrey Sayre-McCord, “Logical Positivism and the Demise of ‘Moral Science'” in The Heritage of Logical Positivism, ed. Nicholas Rescher (University of Pittsburgh Philosophy of Science Series, 1985): 83-92.
Peter Foges, "An Atheist Meets the Masters of the Universe" Lapham's Quarterly (August 21, 2012); Ayer's report on his near death experience, which caused him to reflect, if only momentarily, on his lifelong atheism.
“Logical Empiricism” by Professor Christian Wüthrich, Professor of Philosophy, University of California at San Diego
“A. J. Ayer–Language, Truth, Logic” by Professor Bill Anelli, Dept of Philosophy, Modesto Jr. College
“Ayer, Language, Truth, and Logic (Part 1)” and (Part 2) by Mike Raven, Doctoral Candidate in Philosophy, New York University
The following notes are by Professor Peter Kail, Dept of Philosophy, Edinburgh University:
“A J Ayer Language, Truth and Logic: Lecture One: Introductory”
“A J Ayer Language, Truth and Logic: Lecture Two: The Verification Principle”
“A J Ayer Language, Truth and Logic: Lecture Three: Definitions, Reduction & The Verification Principle”
“A J Ayer Language, Truth and Logic: Lecture Four: Analyticity, Confirmation and Holism”
“A J Ayer Language, Truth and Logic: Lecture Five: Critique of Ethics and Theology”
“A J Ayer Language, Truth and Logic: Lecture Six: Minds”
"The Rise of Logical Positivism" (Part 4-2) and "The Fall of Logical Positivism (Part 4-3)"
"Ayer on Logical Positivism: Section 1", "Ayer on Logical Positivism: Section 2", "Ayer on Logical Positivism: Section 3", "Ayer on Logical Positivism: Section 4" (These are interviews of Ayer conducted by Bryan Magee)
"The Vienna Circle and Logical Positivism"