PROFESSOR McGinn is floating horizontally in his New York apartment, legs straight, his body supported only by his arms. How did we get here, I ask myself, and although Colin McGinn is one of the cleverest British philosophers, it’s not a philosophical inquiry. I’m just trying to work out how we got from the mystery of consciousness, the qualia question (excuse me getting technical), to this demonstration of the professor’s upper-arm strength.

McGinn, a short, robust 53-year-old with a disturbing facial similarity to Anthony Hopkins — and one hell of a pair of biceps — is the author of an acclaimed intellectual memoir, now out in paperback, The Making of a Philosopher. It is beautifully and clearly written and humanises the abstruse discipline of analytical philosophy. Yet it can’t prepare me for this interview, now in its fourth hour. So far he has called his colleagues stupid, told me how gym work can improve my abs, joked that he should get a cut of the profits from the Matrix franchise and acted out a near-death experience aboard a surf-kayak. Philosophy, he explains, is about following a sequence of thoughts to their logical conclusion. In this, I conclude, it does not reflect life. Bertrand Russell could not have predicted the progression of this encounter.

Another “how did we get here?” question is answered by The Making of a Philosopher. It explains how the grandson of two Durham miners, an 11-plus failure, became one of New York’s top philosophers. The answer, like the answer to how you get to Carnegie Hall, is that you practise. Like so many slow-burning intellectuals, McGinn was inspired in adolescence by a teacher, in his case a divinity master, Mr Marsh. Marsh brought up Descartes’ puzzle about how can we know if there is a physical universe if all we have to go by are our internal senses. Might not an evil demon have imposed an entirely false sense of the world in our minds? The Matrix, as McGinn has written enthusiastically from time to time, merely updates this nightmare and adds flying karate.

As a teenager, McGinn spent hours staring at furniture trying to “penetrate the veil of sense data”. The first in his family even to consider university, at Manchester he fell under the spell of the philosopher Dr Wolfe Mays. “I liked,” he wrote, “his open immodesty, his sense of his own importance, as well as his love of showing off.” He went on to Oxford and London universities, embarking on “ a decade of effort”. In 1989 he resigned acrimoniously as Wilde Reader in Mental Philosophy at Oxford and joined Rutgers University in New Jersey, something of a philosophy hothouse. He lives across the Hudson from it in an apartment that he bought ten years ago for $250,000 and that is now worth $1 million.

So getting from Hartlepool to Manhattan is relatively easily explained.

This is more than can be said for the conclusions that his profession tends to reach. If Descartes could make the existence of the whole universe uncertain, Saint Anselm’s “ontological argument”, which also fascinated the teenage McGinn, was able to make God suddenly appear in the room. At this stage in the book (and it was only page eight) I began to feel a queasy foreboding for my own sanity.

Does he ever fear that this way madness lies? “They are way out, some of these things. You wonder ‘Are you thinking about insane questions?’ You become a bit obsessive, of course. I know extremely distinguished philosophers — two in particular, Saul Kripke and David Lewis, who died recently — who are very strange characters. They are not normal by any normal standards.”

Yet he has stayed normal? “Well, with me I think it is because I didn’t start out as a very scholarly type of boy and I still think of myself as having three parts to me. There is my intellectual part, the part most of the world knows about. Then another part of me is sports. I still have a fascination for it and I hope I do tell you a bit about my interest in water sports. (He will, he will.) And then there is also my rock’n’roll side. I have my drum kit in the other room. But these parts rarely enter into my life as a philosopher and intellectual.” A drum kit and a kayak will, indeed, have little purchase on the problem of consciousness — and if consciousness does not strike you as a problem, read his admirable 1999 layman’s book on the subject, The Mysterious Flame: Conscious Minds in a Material World; it soon will.

“Consciousness,” he explains to me, “is such a vague word. It can mean so many things, but what I mean by it is actually just sensation, experience, sentience. So when I look at this, I have a sensation of blue. The problem is if you look in my brain you don’t see a sensation of blue. You see my neurons firing at the back of my brain. The question is, how does that sensation of blue relate to my neurons firing? That’s what people call qualia.”

In 1991 he bundled his work on the subject into a book called The Problem of Consciousness. Its conclusion was that it was an unsolvable mystery. Popular science magazines began to run stories on him; Newsweek noticed; he got labelled, after a rock band, philosophy’s New Mysterian. But much of academia was outraged. Daniel Dennett, of Tufts University in Massachusetts, wrote that he was “ embarrassed to be in the same profession” as McGinn and brought out a book in response, Consciousness Explained. The debate has been feverish ever since, although McGinn’s hunch is that it will peter out quite soon: “Nobody will come up with anything, you see.” McGinn’s well-argued defeatism is dangerous stuff, however, for it touches on a longer tradition of saying that most philosophical questions are equally illegitimate.

Their illegitimacy would explain why, unlike the material sciences, philosophy fails to come up with definitive answers and why one school’s thinking rarely builds on another’s.

So why not just close the book on it? “Well, in a way, you can close the book on it, according to me. But I’m not saying something so radical. Many people have said that in philosophy you are not going to find the answers to questions in the way you do in other areas. But that doesn’t mean that there’s no value in it.”

Because we should know the limits of knowledge? “Exactly. You should understand the limits.”