In short
P.M.S. Hacker (born 1939) is the Oxford philosopher behind the best-known commentary on the Philosophical Investigations, written partly with Gordon Baker. He reads Wittgenstein as showing that philosophical problems are conceptual confusions, applies that lesson to neuroscience, and is a leading critic of the resolute reading of the Tractatus.
P.M.S. (Peter) Hacker is the Oxford philosopher most closely identified with the standard reading of Wittgenstein's later work. Born in London in 1939, he was Tutorial Fellow in philosophy at St John's College, Oxford from 1966 to 2006 and is now an Emeritus Fellow there. Few people have spent as many hours with Wittgenstein's manuscripts.
What he took from Wittgenstein
Hacker took over Wittgenstein's view of what philosophy is for. Philosophical problems, on this view, are not deep questions about reality waiting for a discovery. They are conceptual confusions, knots we tie when we misuse our own words. The job of philosophy is to untie them by giving a clear overview of how our concepts actually work.
Die Philosophie ist ein Kampf gegen die Verhexung unsres Verstandes durch die Mittel unserer Sprache.
Philosophy is a battle against the bewitchment of our understanding by the means of our language.
Philosophical Investigations §109
His slogan sums it up: philosophy adds nothing to human knowledge, but a great deal to human understanding. This is the therapeutic conception of philosophy read as a working method.
What he did with it
His first book, Insight and Illusion (1972), traced Wittgenstein's road from the Tractatus to the Investigations. From 1980 he and Gordon Baker published An Analytical Commentary on the Philosophical Investigations, remark by remark, drawing on the unpublished Nachlass. The first two volumes were joint work; Hacker wrote the later ones alone. In Scepticism, Rules and Language (1984) the two authors argued that Kripke's famous sceptical paradox misreads Wittgenstein on rule-following.
He then turned the method on new targets. With the neuroscientist Max Bennett he wrote Philosophical Foundations of Neuroscience (2003). Its central charge is the "mereological fallacy": saying that the brain sees, decides or believes, when only a whole living person does. Your brain does not read this page; you do. A series of books on human nature followed, from Human Nature: The Categorial Framework (2007) to The Moral Powers (2021).
Where he disagrees
Hacker is a sharp critic of the resolute reading of the Tractatus. In his essay "Was he trying to whistle it?" (2000) he argued that the early Wittgenstein did believe there were truths that can be shown but not said, and that the later Wittgenstein explicitly rejected that picture. He has been equally critical of philosophers who, in his view, turn conceptual questions into empirical ones, among them Daniel Dennett.
His critics, in turn, point to his own style. Wittgenstein worked in fragments and distrusted system; Hacker builds detailed maps of concepts in long, orderly volumes. Even Gordon Baker later moved away from their shared approach towards a more personal, therapeutic reading. Whether Hacker's systematic grammar is Wittgenstein's method carried through, or something more theory-like, remains a live question.
Frequently asked questions
What is the mereological fallacy?
It is the mistake, named by Bennett and Hacker, of attributing to a part what only makes sense of the whole: saying the brain thinks, sees or decides, when these are things a living person does. They argue that much talk in neuroscience rests on this confusion.
Why does Hacker reject the resolute reading of the Tractatus?
He holds that the early Wittgenstein really did think some truths can be shown but not said, and that the later Wittgenstein criticised exactly that view. Reading the Tractatus as pure nonsense with no hidden insights, he argues, does not fit the texts or Wittgenstein's own later remarks.
Sources
wittgenstein.be, “P.M.S. Hacker”, https://wittgenstein.be/en/philosophers/pms-hacker/ (2026-10-20)