Michael Potter is Professor of Logic in the Faculty of Philosophy at the University of Cambridge, and has been a Fellow of Fitzwilliam College since 1989. His forthcoming book, Wittgenstein1916, will be a study of Wittgenstein's views on ethics and religion during the First World War, during the time he was writing his famous Tractatus.

We spoke to him about Wittgenstein, the linguistic turn and the importance of logic to the study of language.

Can you start by explaining what we mean when we talk about the linguistic turn in philosophy?

It is usually attributed to Gottlob Frege in his 1884 book, The Foundations of Arithmetic. He was interested in explaining arithmetic and his account was based on the idea of trying to explain what sentences like "2+2=4" mean. He was worried that merely explaining what a whole sentence means would leave the question answered, but not the question of what really are the numbers?

So he adopted what's called the "context principle". This turned what looks like a metaphysical question, "what is a natural number?" or "what is the number 2?", into a linguistic question about how the word "two" functions in arithmetical questions. So, he adopted this approach for a very specific purpose in the philosophy of arithmetic, but the idea became important in 20th century philosophy. What Frege taught was that when you're confronted with a philosophical question, don't just dive into the question cold. Start by trying to analyse the way that the language is used in the formulation of the question. So, I think that's what the linguistic turn has been taken to mean.

I think, on occasion, the impression has been given that there were a number of philosophers who thought that the method of focusing first on language was the whole of philosophy, that all there is to philosophy is getting clear with how language functions. There was a brief period where there were people thought like that – most notably, Wittgenstein in the Tractatus. But that didn't last long.

Why do you think that Wittgenstein thought that all philosophical questions could be answered by language?

Looking at Wittegenstein, the reason he thought that, in a certain sense, language was all there is to philosophy, was due to his account of what it is for a sentence to be meaningful. The core idea of this was that to say something meaningful, you have to contrast the way you're saying the world is from that which it could've been but isn't. So if you say there's a book on the table, you're making a claim about the world, which may have been false, but isn’t.

Now, he thought that there was kind of a special case, where, if you say something like “either it's raining or it isn't”, that couldn't be false because it's empty, vacuous. It's just saying nothing. He thought that those two cases – contingent cases like "there's a book on the table", or the vacuous claims like "it's raining, or it isn't", exhausted all the proper uses of language.

Now, the thing to think about philosophical claims is that they can't be put in either of those two boxes. They're not contingent claims like "there's a book on the table", and they're not totally vacuous things like "either it's raining, or it isn't." Because those are the only two boxes, the only cache left is not what he thought in the Tractatus, but any claim that cannot be put in either of those two boxes was just … nonsense.

The last idea was then taken up in the 1920s by the Vienna circle, the logical positivists. So, for a period in the 1920s and ‘30s, there were a lot of philosophers who said things like, "the claim that God exists is just nonsense, because it can't be put in either of the two boxes." But that is kind of a brief glimmer in the history of philosophy. They really didn't last after the Second World War. It was a brief period when people tended to have that view.

And where do you think they are mistaken in this?

I think they were mistaken in the basic premise of that view that I mentioned. In that, namely the only way a sentence can make sense is in that contrasted way that I mentioned. So, the later Wittgenstein came to think language was more complicated, that his earlier view had been a crudely simplistic way of thinking about language. I think most philosophers think later Wittgenstein, in that respect, was right. Language is much more complicated.

You’ve spoken previously about the development of modern logic, and its impact on the linguistic turn in 20th century philosophy. Could you perhaps elaborate on that?

I mentioned Frege earlier. Another thing that is sort of due to Frege, and makes him one of the landmark figures in the history of philosophy, is that he invented modern logic in 1879. He invented what's known as "polyadic quantification logic", which is a way of symbolising arguments, but enormously more powerful than anything that had been available in the history of logic for the 2,000 years before him, since Aristotle. So, until Frege, logic had tended to be seen as a trivial subject that couldn't deliver substantial progress. People thought that you couldn’t reach surprising conclusions just by using logic. What Frege did is invent this wonderful new tool, which turned out to be able to get you from progresses to a conclusion that wasn't just trivially obvious from the premise. That was an exciting discovery.

For about 50 years after that discovery, a lot of philosophers were just interested in finding out what it could do. To find out what it could do, what they had to do was symbolise sentences – take sentences of ordinary language, symbolising them using something like the formalism that Frege had given them, and then seeing what logic could do. I think of that as another feature that made the linguistic turn, which explains why the linguistic turn happened when it did, why for a period it seemed so popular. There were a lot of philosophers just wanting to find out what modern logic could do.

You've described how the study of language was seen as the sole role of philosophy only for a brief period in the inter-war years. Subsequently, what do you think the contribution of the linguistic turn has been for 20th century philosophy, through to today

The thing that I think only happened briefly was the idea that it could do the whole job. I think what's still present in many philosophers is the idea that an attention to language can do part of the job. One way to test that would be to look at undergraduate courses in philosophy at universities today. And you'll find that, certainly at the University of Cambridge, but at lots of other universities too, logic is a compulsory part of the syllabus. That's a way of expressing our view that, if you want to make progress in philosophy, one of the basic tools in your tool kit has to be an understanding of how the logic of arguments works. It's a kind of hygiene, like cleaning your teeth every day.

What logicians contribute to philosophy more generally is a kind of clarity of thought, which ensures that you aren't needlessly confused by the accidents of the way that ordinary language works. I think that's still very much present today.

What I was resisting wasn't the importance of logic in philosophy. What I was resisting was the idea that it could do the whole job. I think the normal experience one has as a philosopher is that you use the clarity of thought, as I just mentioned, to strip away the brushwood from a philosophical problem. But then once you've stripped away the brushwood, the problem is still there. It's not been solved by the bit of logical spring cleaning. Of all the traditional philosophical problems I was explaining – how we know about the external world, how we conceptualise our world and understand our place in it – none of those problems have disappeared. The logical spring cleaning doesn't tell you what the correct answer is, but what it might do is show you that there were some answers that people in the past have offered, which are certainly incorrect because they are just a result of confusion.

To conclude, then, the way that the linguistic turn was previously seen as a brave and bold new way of doing philosophy, is there anything we’re looking at now, any new methodologies or ways of thinking about doing philosophy that we can look forward to for having such a radical effect on the field?

Good question. I wish I knew. Off-hand, I can’t think of anything recently which has grabbed me as particularly hopeful. That’s a disappointing thing to say. I suspect maybe it's a sign I'm getting old.

Every few years there's a new fashion that spreads through philosophy, and I suppose I tend to think that many of them are just obviously fashion. Oddly enough, I would say that one of the modern trends of philosophy is in taking the history of philosophy more seriously, rather than less. I think that, at the moment, one of the trends is to recognise that to make progress in philosophy it's important to understand where philosophical problems have come from, and to understand the extent to which our predecessors answered them. But also, to accept what they haven't done and to understand why the answers people offered in the past don't work. Arguably, that's as important as just striking out on your own.