John Lloyd Ackrill, philosopher and classical scholar: born Reading, Berkshire 30 December 1921; Assistant Lecturer in Logic, Glasgow University 1948-49; University Lecturer in Ancient Philosophy, Oxford University 1951-52, Professor of the History of Philosophy 1966-89 (Emeritus); Fellow, Brasenose College, Oxford 1953-89 (Emeritus), Tutorial Fellow 1953-66; FBA 1981; married 1953 Margaret Kerr (one son, three daughters); died Oxford 30 November 2007.

John Ackrill was a leader in the philosophical and scholarly study of Plato and Aristotle. He played a decisive role in forming the dominant philosophical approach to ancient philosophy in the late 20th century.

Born in Reading in 1921, and educated at Reading School (which claims to be the 10th oldest school in England), Ackrill entered St John's College, Oxford, as a scholar in Classics in 1940. The following year he left for war service in the Royal Berkshire Regiment and General Staff, and reached the rank of captain. He returned to Oxford in 1945 to read Literae Humaniores (Classics, philosophy, and ancient history). On graduation, in 1948 Ackrill went directly to a teaching position, as assistant lecturer in Logic at Glasgow.

He was appointed university lecturer at Oxford in Ancient Philosophy in 1949, but before he took up the post he was given two years of study leave, which he spent in Switzerland and in Princeton (which he visited on three other occasions in the 1950s and 1960s). After two years as university lecturer, he became a tutorial fellow of Brasenose College in 1953. From 1959, the other Brasenose philosophy tutor was Michael Woods, a former pupil of Ackrill's, a collaborator in the study of ancient philosophy, and a close friend until his death in 1993.

In 1966, the university created a statutory chair in the History of Philosophy, and Ackrill was elected the first holder. He held it, while remaining a fellow of Brasenose, until his retirement in 1989. As professor he turned from teaching undergraduates to the supervision of graduate students, the provision of graduate classes, and the encouragement of research in ancient philosophy. He was elected a Fellow of the British Academy in 1981, and an Honorary Fellow of St John's in 1996.

In the late 1940s and 1950s, philosophy in Oxford was a lively, experimental, and highly social activity, under the influence – sometimes complementary and sometimes contrasting – of Gottlob Frege, Ludwig Wittgenstein, Gilbert Ryle and J.L. Austin. Ackrill's work combines the older tradition of Oxford philosophical scholarship (represented by Sir David Ross) with his interest in contemporary philosophy. His papers from the 1950s and 1960s use arguments from (inter alios) Peter Strawson, Frege and Ryle, to raise questions about Plato and Aristotle.

Ackrill's role as a college tutor influenced his aims as a teacher and writer. As a tutor, he was, as one distinguished former pupil recalls, "exact but good-humoured". He did not try to persuade a pupil of a particular doctrine, but tried to encourage critical thought through objections and replies. He carried the same Socratic approach into his supervision of graduate students. He would not try to communicate his own position to the student, but would criticise the student's view in ways that would clarify, improve and complicate the position being criticised.

The results of his efforts are evident in much of the best work on Greek philosophy in the past 40 years, both by his pupils and by those he influenced less directly. The character, though not the extent, of his influence may be gathered from the Festschrift produced by some of his former pupils, colleagues, and friends, published in Oxford Studies in Ancient Philosophy in 1986 (edited by Michael Woods).

His Socratic and tutorial attitude appears in his published papers (collected in Essays on Plato and Aristotle, 1997). Often he announces that he aims to provoke discussion, or to raise a problem, not to expound a philosophical system. As he puts it, "it seems to me both enjoyable and rewarding to engage in philosophical argument with Aristotle"; this engagement includes criticism of Aristotle's (or Plato's) errors. His best papers are terse, elegant, bold and challenging. His early short paper "Plato and the copula" argues that Plato sees that central elements of his metaphysical position, and in particular of his Theory of Forms, need to be rethought. In "Aristotle's Definitions of Psuchê", Ackrill argues that Aristotle's familiar doctrines about form, matter and substance rest on conflicting assumptions, and that these conflicting assumptions threaten the coherence of his whole account of soul and body.

His best-known paper – often cited, often translated, and continually discussed since its appearance as a British Academy Lecture in 1974 – is "Aristotle on Eudaimonia", which not only sets out a problem, but also offers a persuasive answer to it He argues that Aristotle conceives the ultimate human good (eudaimonia, often rendered "happiness"), not as some goal that is wholly external to all the activities that we might regard as worthwhile for themselves, to which everything else is purely instrumental, but as a compound of states and activities that are valued for themselves. Ackrill formulates this view with unrivalled clarity, and defends it by close attention to particular passages and difficulties.

His collected papers do not include any of his book reviews or critical notices (which are listed in his Festschrift). These are essential reading for anyone who wants to grasp the range and depth of his interests and his knowledge. His learned, probing, and suggestive reviews and discussions show his expertise and scholarship in areas in which he published nothing more.

In addition to his papers, he published an admirably clear and lively introduction to Aristotle, Aristotle the Philosopher (1981), selections from Aristotle's Ethics with an introduction and brief notes (1973), and an annotated translation of Aristotle's Categories and De Intepretatione (1963). This last work demonstrates Ackrill's remarkable skill as a philosophical translator. Though his notes are said to be "offered only as an aid to beginners", they have provoked many pages of discussion by advanced students as well.

This volume appeared in the Clarendon Aristotle Series, of which Ackrill had become the general editor after the death of J.L. Austin in 1960. The volumes in this series, each of which includes lucid and helpful notes, have made Aristotle more accessible to students at all levels. The individual translators must take much of the credit; the prefaces to their volumes imply that much of the credit must also go to Ackrill, and latterly to his successor, Lindsay Judson.

Many Oxford undergraduates and graduates appreciated Ackrill's lectures and classes; and he supervised many graduate students in Greek philosophy who are now established members of the profession. These are not the only people who have reason to be grateful for his constructive criticism and guidance. Oxford attracts academic visitors from all over the world; and many scholars from outside Oxford, with no formal claim on his time or attention, will recall with gratitude Ackrill's encouragement and advice throughout their careers.

The austere clarity of his writing gives a sense of one side of his personality; but it does not convey the dry and pungent wit that enlivened his conversation, or the warmth and generosity of his friendship.