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The Library of Living Philosophers

Sir Michael Dummett

by Karen Green

Michael Dummett was knighted in 1999, in rather late recognition of his status as a living Oxford monument. Apart from a few years in Birmingham and Berkeley from 1950-6 and occasional visiting appointments in the USA he has spent his professional life teaching and researching in the philosophy of mathematics, logic and language at the University of Oxford. Like the tranquil walk past the Old Bodlean, along the side of Balliol and through the Botanical Gardens that one might take from All Souls College, where he was a fellow from 1950-79, to his home in Park Town, his thought exudes an unhurried richness and has depths which it takes time to fathom.

Usually he is characterized as an anti-realist who advocates the adoption of ‘intuitionistic’ logic, in which the law of excluded middle (“every statement is either true or false”) doesn’t apply. But it is more helpful to think of him as someone interested in the reasons that we might have for adopting realism or some form of anti-realism in various areas. For instance, it is natural to be a realist about the past, that is, to claim that each past-tense statement is either true or false, independently of our capacity to know it. But many people also find it natural to be anti-realist about the future, and to express this by saying that a future-tense statement is not now either true or false. This is the most obvious case in which there is a connection between anti-realism and failing to endorse the law of excluded middle. But how can we justify this difference in attitude towards past and future tense statements? Is it justified by the impossibility of backwards causation? Dummett argues that it is not, but that our acceptance of the asymmetry comes from our believing that it is possible to know the truth or falsity of past-tense sentences independently of our intentions.

Like Wittgenstein, Dummett would like to make the workings of our language transparent and to remove the fog that surrounds it. Unlike Wittgenstein he thinks that it ought to be possible to give a systematic account of what we are doing when we speak and understand a language. Such an account of language will also embody a metaphysical view, an understanding of what kinds of things we are speaking about. Dummett’s thinking about language largely begins from Wittgenstein and from A.J.Ayer’s verificationism. The verificationists used the slogan that ‘only verifiable sentences are meaningful’, to dismiss metaphysics. Dummett, though, argues that verificationism itself embodies a metaphysical view. This is clear in the case of verificationists who also embrace phenomenalism, the view that to exist is to be able to be perceived. Dummett argues that if taken seriously their phenomenalism ought to have led the early verificationists to give up the law of excluded middle.

It is among philosophers of mathematics that intuitionist logic has had its greatest following, and here, too, the failure to assert excluded middle is associated with the thought that numbers do not exist independently of us but are constructed. This is the form of anti-realism with which Dummett has most sympathy, and in his Frege: Philosophy of Mathematics he argues that Gottlob Frege’s logicism can be saved if combined with a more constructivist account of mathematical existence. The thought that we might have reason to revise our logic has also led Dummett to explore the question of the justification of deduction. In opposition to the predominant psychologistic attitude which takes logic to be nothing more than a set of socially established patterns of transition from one sentence to another, Dummett lays the groundwork for an account of the justification of our deductive practice.

It would be a mistake to conclude from all this that Dummett is an other-worldly person concerned only with the most difficult and abstract issues in language and understanding. One of his interests has been the history and rules of card games, and in particular the game of Tarot, on which he has published a number of authoritative works. Following his general tendency to defend reason and to abhor shallow superstition, he demonstrates that it is only since the 1780s that the Tarot has been used for divination, and this use was a piece of quackery with no justifiable basis.

It is in the area of race relations that his most active interventions on behalf of civilized reason have taken place. For many years in the 1960s and 1970s he campaigned actively against racial discrimination. In two books on voting procedures his concern for justice and interest in rules and procedures coalesce. Even in these interests, however, one can detect an echo, and perhaps implicit criticism, of Wittgenstein on following a rule.

Karen Green is the author of Dummett: Philosophy of Language (Polity, 2001) and The Woman of Reason: Feminism, Humanism and Political Thought (Polity, 1995). She lectures in Philosophy at Monash University in Australia.

• The Philosophy of Michael Dummett, in the Library of Living Philosophers Series, is edited by Lewis Hahn and published by Open Court Press.