J.L. Ackrill, Professor of the History of Philosophy at Oxford, 1966-89, was one of the leading figures of the 20th century in the study of Ancient Greek philosophy.

Claims about new beginnings and fresh starts in an academic discipline are sometimes too easily made. But in the late 1950s and the 1960s there was indeed a sea change in the study of ancient philosophy, thanks to Ackrill and a small handful of others, most notably Gregory Vlastos and Gwil Owen. It involved the conviction that one must bring to bear on ancient texts not only meticulous classical scholarship — that was not new — but also the utmost philosophical rigour and acuity.

This revolution was prompted in part by the rise of so-called “ordinary language philosophy” and the interest sometimes displayed by Aristotle (though rarely by other Ancient philosophers) in appealing to “what we say”, which suggested a close community of interest between him and contemporary philosophers such as Austin and Ryle. The approach of Ackrill and others was not, however, restricted to the ordinary language perspective: the central idea was, as it remains, that of combining textual sensitivity with vigorous philosophical engagement.

John Lloyd Ackrill was born in 1921. He was educated at Reading School, and went up to St John's College, Oxford, as a Thomas White scholar in Trinity Term 1940. There he formed a wide circle of acquaintances, including Kingsley Amis, John Wain, John Wilton and Leader Hawkins.

After he had taken a first in Classical Mods his undergraduate career was interrupted by war service, which included a period with the General Staff in the somewhat unlikely role of a motorcycle dispatch rider in France — once memorably bearing a message for Field Marshal Montgomery in one pocket and a vial of cyanide to be taken in case of capture in the other.

In Berlin in 1945 he was given early release to return to Oxford, where he took a first in Greats in 1948. His first academic post was as assistant lecturer in logic at the University of Glasgow, and after a year he was appointed to a new university lecturership in Ancient Philosophy in Oxford. This came with an initial two-year study leave, which he spent first in Switzerland and then at the Institute for Advanced Study in Princeton, where he worked with Harold Cherniss. He was to make several more visits to Princeton over the next decade, and developed a close friendship with Gregory Vlastos.

In 1953 he was elected to a tutorial fellowship and university lecturership at Brasenose College, Oxford, and in August of the same year married Margaret Walker Kerr. His undergraduate pupils at Brasenose included David Wiggins and Michael Woods. Woods was later elected to a fellowship at Brasenose: and if Oxford was the place to be for Ancient Philosophy in the 1960s, 1970s and 1980s, the team of Ackrill and Woods made Brasenose the place to be in Oxford. In 1966 Ackrill became the first holder of Oxford's Professorship of the History of Philosophy.

Although Oxford professorships are each associated with a particular college (in this case Keble), Ackrill's great attachment to Brasenose led him to take advantage of a curious Oxford rule which allowed the first holder of a chair, if already associated with an Oxford college, to remain there — somewhat disconcerting Austin Farrer, the Warden of Keble, in the process. Ackrill served as vice-principal of Brasenose, 1978-80, was made a Fellow of the British Academy in 1981, and continued as Professor of the History of Philosophy until his retirement in 1989. He was made an honorary Fellow of St John's in 1996.

He oversaw a generation of graduate students, in his regular graduate classes on Plato and Aristotle (and occasional ones on Plotinus), as a doctoral supervisor, and as adviser to a stream of visiting students from all over the world. A review of his first book, on Aristotle's Categories and De Interpretatione, captured Ackrill's particular style as an Ancient philosopher: “Mr Ackrill never raises his voice.”

Ackrill disliked any form of showiness, and had a passion not only for precision in thought and speech but also for clarity and simplicity of expression. He had a deep distrust of any attempt to be definitive: it was highly characteristic of him to describe his own work as merely pointing out or clarifying problems; and some of his work is indeed principally of this character, such as his enormously influential 1973 paper Aristotle's Definitions of Psuche, and his excellent introduction to Aristotle, Aristotle the Philosopher (1981).

Other papers, such as his ground-breaking articles on Plato's Sophist and his renowned British Academy lecture on Aristotelian eudaimonia, display a less Socratic style; but even here Ackrill always steered clear of grand systems and the sweeping statement, preferring to work on texts and problems in all their particularity, and possessing an extraordinary ability to go to the heart of things with great concision and the minimum of fuss.

He was the ideal person to take over the Clarendon Aristotle Series from its founder, J.L. Austin, on the latter's death in 1960. The aim of the series, which Ackrill was to edit for more than 40 years, was to present accurate translations of Aristotelian texts, and philosophical commentaries designed to help readers to think about these texts for themselves. The second volume to appear, in 1963, was Ackrill's own on the Categories and De Interpretatione, two early works concerned with foundational issues in Aristotle's philosophy of language and metaphysics. Ackrill's translation set a standard for faithfulness and elegance which few others have equalled; his illuminating and incisive commentary has been among the main stimuli for work in these areas over the last 40 years. The book is one of the most cited works on Ancient Philosophy in the English-speaking world.

He retired as editor in 2001, having overseen the writing of 19 other volumes, and having thus been the prime mover in the creation of an unrivalled resource for professionals as well as graduates.

In his personal life Ackrill displayed the same qualities found in his academic work. What colleagues found most striking about him was his modesty, his courtesy, kindness and unfailing good humour, a Socratic seriousness coupled with a quiet wit, and his love for his family: however much philosophy was discussed, the conversation always turned at some stage to Margaret and their children.

It was entirely characteristic of Ackrill's approach to ancient philosophy that he began the last paragraph of the final essay in the second edition of Essays on Plato and Aristotle (2001) with “I end on an interrogative note.” What Ackrill did for a whole generation of ancient philosophers, as his writings continue to do for his readers today, was to teach them — and inspire them — to be interrogative; to ask searching questions of difficult texts.

He is survived by his wife, Margaret, and their four children.

Professor J.L. Ackrill, philosopher, was born on December 30, 1921. He died on November 30, 2007, aged 85