Books: Waltzing to a Viennese air - A J Ayer: a life by Ben Rogers Chatto & Windus, pounds 20, 407pp

IN 1936, Language, Truth and Logic, by the 26-year-old Alfred Ayer, was a succes de scandale. The Master of Balliol, when his students proposed discussing the book, picked up a copy and threw it out of the window. The philosophical world was "humming like a beehive that has been kicked". Ayer, asked what he was going to write next, gleefully replied, "There's no next. Philosophy has come to an end. Finished." But it struggled on, and 40 years later, asked by Bryan Magee about the book's faults, Ayer said: "Well, I suppose the most important defect was that nearly all of it was false."

Odd that the falsity of his most celebrated book should be cheerfully acknowledged, but then philosophy is odd. Although it is dedicated to the pursuit of truth, the attainment of truth is not an essential criterion of a philosopher's merit. Ayer was a force to be reckoned with in British philosophy. He changed its course, some would say for the worse.

Ayer was happy to admit that Language, Truth and Logic was not original but an exposition of the Logical Positivism of the Vienna Circle, which he frequented after graduating from Oxford. "The meaning of a proposition is its method of verification" was the slogan of these scientifically- based philosophers. If the truth of a statement cannot be tested empirically, it is meaningless. In lucid prose and with a young man's "swashbuckling" delight in debunking, Ayer wielded this Occams's razor to slash away vast swathes of what we normally believe.

Moral judgements are nothing more than expressions of emotions; history probably is bunk (past-tense statements being unverifiable). Although Ayer later moderated these extreme counter-intuitive views, he always adhered to the empiricism that inspired them. Ted Honderich, in a memorial address, acclaimed him as a "hussar against nonsense," but Roger Scruton saw him as slaying "the conception in which the wisdom of humanity reposes".

An only child, Ayer grew up in North London, and went to Eton and Christ Church, Oxford. His father (secretary to the banker Alfred Rothschild) was French Swiss, his mother came from the Dutch-Jewish Citroen car family. "I'm always on the outside, on the outside always looking in," he was once heard to intone, and, for all his philosophical acclaim, media popularity, knighthood and professorships, he confessed to being forever afraid of being denounced as a fraud or told "underneath you are a dirty little Jewboy".

Insecurity tended to make him bumptious and vain, intensely competitive in every area from philosophical debate to sexual conquest (for which he was equally notorious), from finishing the Times crossword to scoring in cricket. He needed to verify himself. His second (who was also his fourth) wife considered him virtually autistic in his lack of feeling for others. Indicatively, the philosophical problem he found most intractable was that of other minds.

But Ben Rogers manages to convey, with a fine mixture of sympathy and stringency, how extraordinarily loveable he was, despite his egoism - vital, funny, charming, courageous, and with the egoist's gleeful, uproarious childishness. He was an outstanding teacher. If the reader has the sense of forever seeing Ayer from the outside, it is hard to portray someone's inner life when there was so little of it. Ayer kept few letters, and those he wrote, are mostly, like his autobiography, mundane, unrevealing and emotionless.

Rogers claims that no philosopher, at least in English, was so adamant to distinguish philosophy from life. Cyril Connolly said there were two Freddie Ayers, the Oxford philosopher and the London dancer. Yet surely few other philosophers so fitted the philosophy they espoused. The philosophy's clever, stylish shallowness mirrored that of the man. Lacking a sense of inner self, or of connection to others or to nature, Ayer really did live as a Humeian "bundle of perceptions".

The stern abrogation of the spiritual by a religiously troubled philosopher like Wittgenstein (or Russell) has the noble self-denial of asceticism as practised by a sensualist. Their natures were at odds with their philosophies, which are informed by what they deny, and correspondingly deep. Ayer's total, crossword-puzzle verbal literalism, however, made him as blind to transcendent mysteries as he was lacking in visual sense. Asked what he saw when he thought of Paris, he answered "a sign saying Paris".

Of course, he could happily pronounce as meaningless propositions about God or metaphysics; so does the brash monoglot dismiss foreign tongues. Even his skill at dancing seems more than metaphorically applicable; it was agility in argument in which he excelled. Unlike Wittgenstein, ultimately he could not break down compartments in philosophy. He kept within the bounds of pre- established harmonies, for all his apparent iconoclasm.

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