Do we have positive reasons to think the world itself is contradictory? Is there an essence to philosophy that holds across all its different styles and traditions? What do recent developments in AI mean for the philosophy of mathematics? Graham Priest — logician, metaphysician, and the world’s foremost defender of dialetheism, the view that some contradictions are true — answers these questions and more in this written interview with The Curious. Burak Öztürk asked Priest 14 questions ranging from artificial intelligence to the history of philosophy to dialetheism itself, each framed within the wider arc of his philosophy.

Burak Öztürk: When we look at early-modern philosophers — rationalists like Descartes and Leibniz, but also empiricists like Hume — we see that they take classical logic for granted: metaphysics is assumed to obey the principles of classical logic, as if the world’s structure itself follows those rules. Today, apart from classical logic, we have many different kinds of logics. As both logician and metaphysician, what do you take the relationship between logic and metaphysics to be? Is there a logic uniquely suited to metaphysics, if there’s one at all?

Graham Priest: First, what is now called classical logic was invented only at the end of the 19th century (by Frege, Russell, and others). The orthodox logic in the period you mentioned was Aristotelian Syllogistic. This is quite different from classical logic. For a start, it is paraconsistent, as Aristotle himself points out.

It is clear that there is a dialectical relationship between logic and metaphysics, since some logics are incompatible with some metaphysical views¹. To articulate a metaphysical view that is correct, one must use the correct logic, and vice versa. Clearly, determining a correct metaphysics and a correct logic must go hand in hand.

The law of non-contradiction has traditionally been treated as the paradigm case of an analytic, a priori truth. Given that your work denies its universal validity, does dialetheism force us to give up the analytic/synthetic distinction altogether — or can the distinction survive once its paradigm case is removed?

The principle of non-contradiction has indeed been highly orthodox in Western logic, though there have been dissenting voices, such as Hegel. (The principle is much less orthodox in Eastern traditions.) The analytic/synthetic distinction is perfectly compatible with dialetheism. One may hold, for example, that the principles of deductive logic are analytic. So what is analytic will be at least in part determined by the correct logic. One may disagree about that matter, and so about what is analytic.

In the preface to One you describe dialetheism as “a metaphysical view” — as opposed, presumably, to a merely technical or instrumental use of paraconsistent logic. That’s a different contrast from the semantic/metaphysical distinction I’m asking about here: is a dialetheia a fact about language, or about the world itself, independent of how we describe it? Given both distinctions, where would you place yourself?

Dialetheism is the view that some contradictions are true. What makes something true? Consider the statement that Canberra is the federal capital of Australia. This is true; what makes it so? First, this depends on the meanings of the words‘capital’, ‘Australia’, etc. But meanings alone are not sufficient. There are also facts about the history and geography of a large island in the Southern Hemisphere of out planet. In other words, in general, truth is dependent on facts about language and facts about reality—the non-linguistic world if you like. Dialetheias are not different from other truths.

Beyond its power to resolve paradoxes like the Liar, are there positive metaphysical reasons to think reality itself — not just our formal treatment of it — might be inconsistent? Or is the case for dialetheism ultimately a technical one, about what it lets us prove? In other words, would (metaphysical) dialetheism provide a better understanding of the world?

Whatever your views on idealism, realism, etc, to understand reality, you have to understand what is true. Quite generally, understanding what is true provides understanding of the world. (See the last question.) Dialetheias are no different from any other kinds of truth in this regard.

In July 2025, experimental models from OpenAI and Google DeepMind each solved 5 of 6 problems on that year’s IMO at gold-medal level. Does a result like this bear on how we should think about Gödel’s incompleteness theorems — say, on debates like the Lucas–Penrose argument about minds, machines, and provability? Does it change anything in the philosophy of mathematics?

No. AI algorithms are just theorem-provers, just very powerful ones. So there is nothing new here. And the Lucas-Penrose arguments were always terrible anyway².

Some philosophers — Rorty’s “four genres” essay is the classic statement of the problem — have argued that history of philosophy has a strange status: doing it well seems to require doing philosophy itself, in a way that, say, history of physics doesn’t require doing physics. Is that actually right, or does philosophy just share this feature with fields like mathematics, where old proofs stay live rather than superseded? And if philosophy really is different here, what do you think explains it?

Well, doing the history of philosophy can mean different things. It could mean mining the ideas of past philosophers to find insights in them which can then be applied to live issues. Philosophers do do that, and I think it is rare to find this in other disciplines. (Why philosophy is distinctive in this way is an interesting question.) On the other hand, it could also mean interpreting what historical figures said and achieved. That is straight history. All intellectual inquiries have such a history. However, in any such enterprise there is always a certain kind of principle of charity at work: the views are interpreted in as plausible a way as possible, even if they are wrong. And plausibility often does require engagement with the contemporary state of the discipline. I think this would be the case in the history of any subject.

In the preface you say Beyond the Limits of Thought isn’t a history of philosophy book, yet it reads as a distinctive survey of world philosophy, and the whole project seems to function as a kind of support for “metaphysical” dialetheism, even without defending it outright. How would you describe the book’s methodology? To me it reads almost like an induction, but over theories rather than particular cases. Does that fit?

It does both of the things I mentioned in the last answer. it mines the history of philosophy for ideas which support and inform contemporary debates, namely, of course, that concerning dialetheism. At the same time it puts ideas in the history of philosophy in a new context and perspective, so that they can be seen in a new way.

Last year you taught a course on Avicenna at CUNY. What was it like engaging closely with Islamic philosophy? Did anything in his system strike you as genuinely dialetheic, rather than merely apparent contradiction?

Engaging with Ibn Sina was the same as engaging with any other philosopher I have taught, about about whom I knew little before the course—and that includes many other Western philosophers (yes, Arabic philosophy is an integral part of Western philosophy), and many Asian philosophers. There are certainly dialetheic tendencies in the medieval Arabic and Latin philosophers who are influenced by Neo-Platonism; but Ibn Sina is not one of these. He is a pretty straight Aristotelian.

You’ve argued that Hegelian and Marxist dialectics involve genuine dialetheias rather than metaphorical tension. What do you think made dialectical thinkers receptive to literal contradiction in a way the mainstream Western tradition after Aristotle generally wasn’t? And is dialectical method the only route by which a philosopher lands on dialetheism, or do you see Hegel and Marx as one path among several — alongside figures like Cusa, or traditions like Buddhist logic?

Where Western philosophers were dialetheists before the 20th century, this was largely because of the influence of Neo-Platonism, which is clearly dialetheic. The list of such philosophers includes Ibn Arabi, Meister Eckhart, Cusanus, Hegel, and Heidegger. The last two are not normally thought of as in that tradition, but they have exactly a Neo-Platonist problematic—whether they admit/realise this, or not. There is an absolute that creates (the rest of) reality, including people, so that it, in the guise of people, comes to understand what it is³. The exact role that contradiction plays in the philosophy of these thinkers can vary quite a lot. Dialectics, and the role that contradiction plays in this, is distinctive of Hegel (and to a much lesser extent, Marx).

All of these thinkers had reasons which drove them to dialetheism, but there are many others, as some of the Eastern traditions and contemporary Western philosophy have shown⁴. One that has taken up a good part of the contemporary literature concerns paradoxes, such as those of self-reference.

You’ve argued that Hegelian contradictions should be read as literal dialetheias, not metaphorical tension. On the other hand, Robert Brandom reads Hegelian “contradiction” quite differently from you — as tensions between commitments that get resolved through more precise specification of concepts, not as literally true contradictions. Does his reading pose a real challenge to yours? What does it miss, if anything?

I have not studied Bob’s work on Hegel, so what I can say is very limited. First of all, I do not deny that Hegel often uses the term ‘contradiction’ in some sense other than the logician’s. Next, in A Spirit of Trust, Bob reads Hegel’s Phenomenology as endorsing and articulating many of the theme’s in Making it Explicit. That may well be true: I have never thought much about it. However in other places Hegel clearly and explicitly endorses contradictions, for example in his account of motion in the Logic and his account of Eubulides in the Lectures on the History of Philosophy. So Hegel is clearly a dialetheist. Where Bob and I may part company is in the role of contradiction in the dialectic of the Logic. As far as I know, Bob has no extended discussion of this in his work, but there are systematic reasons, both historical and textual, why dialetheism appears to play an important role in this. Contradictions arise and are aufheben—and it should always be remembered that this means both ‘removed’ and ‘preserved’⁵.

Professor Priest, you have a quite wide research of philosophy, ranging from Analytic to Continental to Buddhism. Do you think the differences between these traditions/schools are substantial? In your Inaugural speech “The Nature of Philosophy and Its Place In The University” you determine the essence of philosophy as “self-reflexivity”. Does this apply to all philosophical traditions? If so, what are the main differences between these traditions?

The thinkers in each of these “traditions” show enormous variety, both stylistic and doxastic. Contrast Wittgenstein, Austin, and Singer; or Nietzsche, Gadamer, and Derrida; or Nāgārjuna, Huineng, and Dōgen. And often thinkers in different “traditions” are closer to each other than they are to other thinkers in the same “tradition”. Compare Kuhn and the early Foucault, or Quine and Derrida on their attacks on the determinacy of meaning; and Stoic ethics has much more in common with Buddhist ethics than it does with Kantian ethics. So I think it is inadequate scholarship to categorize philosophers in this simplistic way, or to expect to find very significant differences.

In the lecture you mention, I argued that it is distinctive of philosophy, unlike other inquiries, that it concerns its own nature, and I still think this is right. Great philosophers, from all “traditions” were concerned with the nature of philosophy: Plato, Ibn Sina, Kant, Wittgenstein, Quine, Nietzsche, Husserl, Heidegger, Zhuangzi, Nāgārjuna, Dōgen—though in most of these philosophers, the issue is mixed up with the discussion of rational thought more generally.

What is the benefit of reading and comprehending different philosophical traditions, as a philosopher? Is there a risk in this kind of comparative work, such as flattening real differences between traditions to make them legible to each other? Where do you think it goes wrong when philosophers do it badly?

As you can guess, I’m not fond of thinking of philosophy in terms of traditions. Philosophy is written in many styles, voices, and languages. Great philosophy can be in any of these—as can poor philosophy. No philosopher is right about everything, but great philosophers have insights from which one can learn. The more insight one has, the better one is able to address philosophical issues.

What can go wrong when this is done badly? Probably many things; but thinking can degenerate into: Aristotle said this… Confucius said that… That’s not philosophy. That’s journalism. Nor does it help to say ‘Gee, didn’t they say similar things sometimes’. You’d expect thoughtful philosophers to say similar things sometimes.

You’ve practiced karate to a high level and you’ve also co-edited two books putting philosophy and the martial arts in direct conversation. Has that practice actually shaped how you think about contradiction and the unity of opposites, or do you keep the two separate?

No. Karate has had an effect on the way I think about many philosophical matters: the mind/body relationship, ethics and how to treat people, how to teach. None of these has any direct bearing on dialetheism.

We know you come from a working-class background, as do most of our readers. What would you suggest to those who want to pursue a career in philosophy? How can making such a career path less costly be achieved?

Clearly, a rich kind grows up with a head-start on many things in life, and a poor kid will always be coming from behind the pack, but persistence and determination go a long way. And most people will have good fortune sometimes: perhaps someone who is prepared to go out of their way to help, scholarships and other forms of funding, unexpected educational opportunities, opportunities to travel. Use these wisely. And when you can, help others in the same way.

Notes

1. See my ‘Metaphysics and Logic: an Observation in Metametaphysics’, Giornale di Metaphysica 1: 68–77 (2019). ↩︎
2. See my ‘Gödel’s Theorem and the Mind… Again’, in Philosophy of Mind: the place of philosophy in the study of mind, eds. M. Michaelis and J. O’Leary-Hawthorne, Kluwer, 1994. ↩︎
3. See Part III of my Nothing in Particular, Oxford University Press, 2026. ↩︎
4. See my In Contradiction, 2nd edition, Oxford University Press, 2006, and The Fifth Corner of Four, Oxford University Press, 2018. ↩︎
5. See my ‘Kant’s Excessive Tenderness for Things in the World, and Hegel’s Dialetheiesm’, ch. 2 of S. Lapointe (ed.), Logic from Kant to Russell: Laying the Foundations for Analytic Philosophy, Routledge, 2019. ↩︎