David Pears, who has died aged 87, was an important figure in British philosophy from its heyday in Oxford after the second world war, when ordinary-language philosophy was just beginning to flourish. He helped set the parameters for the study of Ludwig Wittgenstein with his three books and many articles on the philosopher, and also wrote extensively on Bertrand Russell and David Hume, and on topics in the philosophy of mind, metaphysics and philosophy of language.

It is less easy to pin a particular set of doctrines on him than on some of his illustrious friends and contemporaries (Peter Strawson, Michael Dummett, Elizabeth Anscombe), but the philosophy of mind would have looked different without him, and arguably, thanks to the self-effacing balance of his approach, he was "the only Wittgensteinian to get Wittgenstein right", as a fellow Wittgensteinian said. A professor at Christ Church, Oxford, Pears held visiting professorships at the University of California Los Angeles (UCLA), Berkeley, and other American universities.

He went to Westminster school, where the philosophers Richard Wollheim and Patrick Gardiner were fellow pupils and became lifelong friends. He was in the Royal Artillery during the war, and was seriously injured in a practice gas attack. On demobilisation, he studied classics at Balliol College, Oxford, and developed an interest in current philosophy thanks to a lucky accident.

As he fled the Randolph hotel after being assaulted by a beefy baronet, Pears broke his leg, and, as he was being carried to the ambulance, grabbed a book from a friend to read in hospital. It was Wittgenstein's Tractatus Logico-Philosophicus, which, he said, changed his life, and which he later translated in collaboration with Brian McGuinness, theirs becoming the canonical version.

Marked out as brilliant from a young age, he became research lecturer at Christ Church soon after graduating in 1948, and his early papers were included in Antony Flew's collections of cutting-edge linguistic philosophy, but he was strangely diffident, and (at first) always needed a glass of Guinness and two digestive biscuits before giving a lecture. In the 1950s, he, Strawson and Mary and Geoffrey Warnock, all starting out on their philosophical careers, staged a series of debates on what was then the Third Programme, which were later adapted into three books.

In the 1960s, he found himself "driven to the conclusion that there must be a causal connection between desire and action, because there seems to be no other theory that fits the phenomenon". Although this line went drastically against the prevalent Wittgensteinian doctrine that reasons cannot be considered causally, it soon became fashionable. Except for the odd mention of Pears, full credit for it has gone to the American philosopher Donald Davidson, who went on fully to develop the causal theory of action. This is characteristic.

Pears was not, or never seemed to be, ambitious, apart from his desire to get to grips with problems that interested him, irrespective of glory. He pursued philosophy for its own sake wherever it led him, said a fellow academic, with total "purity of philosophical motive". For him, philosophy was an exciting joint enterprise, and far from being competitive, he loved fostering the work of students and colleagues, sending them congratulatory postcards from wherever he happened to be, although inevitably he had his quarrels too. Perhaps he never quite attained the stature expected of him, being less influential through his writing than through brilliant, witty discussion, and something of an unsung hero. He would rather self-deprecatingly say that he owed his entire intellectual achievement to his extraordinary photographic memory.

When his book Ludwig Wittgenstein was published in 1971, Igor Stravinksy wrote to congratulate Pears on the beauty of his writing, which, wrote Bernard Williams, "combines in a very pure form the more conversational and the more formal aspects of analytic philosophy (it is rather reminiscent of a certain kind of 20th-century French music)". For Williams - they had given a fascinating seminar on identity together in the 1950s, which was described as "the high-point of philosophical activity of the time" - Pears's questions and discoveries, which were often "deliberately, and realistically, vague", were "constantly shaped ... by a project of self-understanding".

Fascinated by paradox, expert in psychology as well as philosophy, and with an insight and empathy unusual in academic males of the time, Pears wrote brilliantly on the self, self-deception and weakness of will. Philosophers, he complains in Motivated Irrationality (1984), tend to ignore that reason "is a force that is stronger in some people than in others" and "project into ordinary thought and behaviour the rationality of their own analyses of ordinary thought and behaviour", adding, "their prejudice is common among bystanders, who forget what it is like to be a participant".

One reason that he loved, and linked, Hume and Wittgenstein was the aspiration he ascribed to each of them of understanding humans as they are, grounded in fleshly reality. "Wittgenstein's case against philosophical theories," he writes in the second volume of The False Prison: A Study of the Development of Wittgenstein's Philosophy (1988), is "that they are postulates of reason", whereas he himself is trying to "make us see how our own linguistic devices work, simply by putting them in their place in our lives ..."

It was exhilarating to be taught by Pears. He often took on students whom other dons were wary of, arguing that you could never tell who his students were, since they were not carrying on some line of his, but developing their own interests. Spotting nonsense was his great strength; he was a "balloon-pricker", as one friend said. With his eye for the absurd, and sense of the fantastical, he was life-enhancingly funny and a brilliant raconteur, telling stories in so frank and ingenuous a way that it was hard to tell, and hardly seemed to matter, whether they were true or not. He and Isaiah Berlin seemed to think that the whole point of life was to make one another laugh, said a friend. He knew everyone, and the gossipy part of philosophy was his meat and drink.

He believed that he did his best work when in a good mood, and, as visiting professor to UCLA (1979), would drive to the beach each morning and sit by the sea, writing and watching people and dolphins. Passionate and erudite about art, he was influential in setting up the Christ Church Gallery.

He and Mary Warnock shared a love of interior decoration, and scoured obscure shops for fabulous materials when given the task of decorating a philosophy hang-out by John Austin, whose famous Saturday mornings in the 1950s they both attended. Before his marriage to Anne Drew in 1963, he and the Warnocks would go on holiday together in Italy, the Warnock children finding him hilarious, and he taking them completely seriously.

His own idyllic childhood summer holidays in a house near Salcombe in south Devon (which he tried to recreate for his son and daughter) left him with a love for botany and of studying butterflies and moths. He inherited a butterfly collection from an uncle, which he considerably added to, until, dismayed by seeing the light fade from a moth's eye, he decided not to kill them, but to photograph them instead. He used to dispatch male Emperor moths from his house near Oxford to mate with females in the garden of Patrick and Susan Gardiner, three miles away - and it worked.

Skilled at cooking, gardening and carpentry, he was always practical and quick-witted - when he arrived at the scene of a car accident in the High, Oxford's high street, he instantly tore up his shirt into bandages while his philosopher companions merely dithered. Always, perhaps, he was trying to follow the advice of his beloved Hume: "Be a philosopher but, amid your philosophy, be still a man." He is survived by Anne and his children.

• David Francis Pears, philosopher, born 8 August 1921; died 1 July 2009

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