This book is perfect for someone who wants to find out what philosophy is all about. First of all, it's very short. Secondly, it's written in prose that is completely unpretentious, unpatronising and clear. It's the kind of book you could read in an evening, but at the same time you'd really have a flavour of what philosophy is. It's got the authority of him being a significant philosopher in his own right, but if you had no idea who he was it wouldn't matter. The writing is almost Orwellian in its simplicity and directness. As somebody who has tried to write clear introductory books, I know how difficult that is to pull off.

Nagel begins with the observation – which mirrors my experience as a teacher and as a father – that philosophy arises naturally out of the human condition. People start asking philosophical questions from an early age. And there is a history of over 2000 years of people discussing these questions – thinking critically about how we should live, what the nature of reality is, what consciousness is. Nagel goes through all these major areas of philosophy with a very light touch.

“What does it all mean?” is a question that people who haven't studied philosophy often think the subject is about. They might be a little disappointed, if they study it formally, to discover that there is little talk about the meaning of life and so on. Do you think the title might give readers false expectations?

In the introduction to the book, Nagel writes, "There isn’t much you can assume or take for granted. So philosophy is a somewhat dizzying activity, and few of its results go unchallenged for long." He's not pretending philosophy is going to tell you what it all means. It's going to introduce you to the questions and help you think critically about them. If somebody comes to philosophy thinking they are going to come out after a few years understanding exactly how we should live and what reality is like, then they're naive. That's one of the things you learn from studying philosophy. As Socrates pointed out, true wisdom lies in knowing how little you know.

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Edward Skidelsky recommends:

Plato is the founding figure in the Western philosophical tradition and The Symposium is one of his most charming books – you can read it like a novel. It’s set in the house of an Athenian, who has invited Socrates and some of his other friends around after a theatrical event for a drinking party. They’re chatting, and they each give a speech where they set out their concept of “Eros”. The one everyone remembers is the speech of Aristophanes, the comic playwright, who says that originally human beings had four legs, four arms, and two heads, and then Zeus broke us in two. So we’re all going around looking for our other half and when we find it, we will feel complete again. It’s a little twee, and it appeals to our romantic sensibilities, but it isn’t actually Plato’s idea of Eros at all.

His idea is that Eros is a desire for “the good” itself, and that we only desire an individual insofar as he appears to us to embody the good. Ultimately, sexual love is a kind of misdirection of this desire for the good, which we’ve got to transcend. I’ve become fascinated with this idea, because I think it explains a lot of problems to do with moral motivation. A lot of people think that in order to motivate somebody to behave morally, you’ve basically got to make it in their interest, by setting out some system of rewards and punishments. But what Plato seems to be saying is that moral education is not a matter of imposing principles on people against their natural bent, it’s more a matter of engaging with their desires and educating them ­– leading them towards the good. And that, I think, is very attractive and important.

Plato was Socrates’s disciple and Aristotle’s teacher. What was Aristotle’s thinking about virtue?

Aristotle was Plato’s most famous student. The Nichomachean Ethics is a sophisticated and subtle analysis of the various virtues – courage, temperance, and wisdom among many others. It’s incredibly subtle and precise, especially when you compare it with the way a lot of moral words are used today.

I was struck by Aristotle’s description of courage in particular. The word as it’s used today by journalists and politicians has almost no meaning at all. People will say that some writer who wrote a very revelatory book about his son’s drug addiction showed incredible courage, or that someone who stands in the middle of Trafalgar Square and masturbates as part of some artistic performance shows real courage. And suicide bombers are “cowards”, which is the one thing they are not. We use the words “cowardly” and “courageous” very loosely – really just to express the fact that we approve or disapprove of something. Whereas Aristotle says courage is overcoming fear of something. Not just fear of anything, there are some things which you should feel fear about, like disgrace – so someone who overcomes their fear of disgrace is not being courageous, they’re just being shameless.

Aristotle also talks about the virtues as being means between extremes. So wit is a mean between the vice of deficiency, which is boorishness, and the vice of excess, which is buffoonery. Most modern moral philosophers would think that there’s nothing really to be said about wit – it’s just a matter of subjective opinion or preference, not something you can analyse or discuss rationally. But Aristotle shows that you can say quite a lot about it that is really plausible and persuasive.

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Brian Leiter recommends:

The virtue of this book is that it has a detailed and readable narrative of Nietzsche’s life, but it combines it with an introduction to his philosophical works, which is written at a very appropriate level for the beginner.

There’s a famous quote in Beyond Good and Evil where Nietzsche says that despite philosophers’ claims about arguing rationally and aiming to find objective truth, all philosophy has really been a form of unconscious and involuntary autobiography. How do you think Nietzsche’s own life informs his philosophy, if at all?

The influences of Nietzsche’s own life on his philosophy are very dramatic. Some of them have to do with the intellectual biography, of course – what he studied, what he read et cetera. But I think probably the crucial fact about Nietzsche’s life is that when he writes about suffering he’s not a tourist. He’s writing about something he knows very intimately. He understands from his own experience the effect of suffering on the mind, on creativity and on one’s attitude to life generally. And if there’s a central question in Nietzsche it’s the one he takes over from Schopenhauer – namely, how is it possible to justify life in the face of inevitable suffering? Schopenhauer comes up with a negative answer. He endorses something like a stereotype of the Buddhist view: The best thing would not to be born, but if you’re born the next best thing would be to die quickly. Nietzsche wants to repudiate that answer – partly through bringing about a re-evaluation of suffering and its significance.

Could you give a sense of the suffering Nietzsche experienced and why his life was so difficult?

He was the proverbial frail and sickly child. But the real trouble started in his early thirties, the 1870s, when he started to develop gradually more and more physical maladies – things that looked like migraines, with nausea, dizziness, and he would be bedridden. It got so severe that he had to retire from his teaching position at the age of 35. So he spent the remainder of his sane life, until his mental collapse in 1889, basically as an invalid travelling between different inns and hotels in and around Italy, Switzerland and southern France, trying to find a good climate, often writing, often walking when his health permitted, but often bedridden with excruciating headaches, vomiting, insomnia. He was trying every self-medication device of the late 19th century. He had a pretty miserable physical existence. His eyesight also started to fail him during this time. Through all this he usually managed to continue to write and read, despite these ailments. So he really knew what suffering was.

In retrospect, there’s reasonably good evidence that he had probably at some point contracted syphilis and that the developing infection might have been responsible for these maladies. Though his father had also died at an early age, so there may have been some familial genetic component as well.

It seems like Nietzsche is one of the few philosophers whom lots of people who have never studied philosophy still enjoy reading. Why do you think he’s so appealing?

I think the most important reason to start with is that he’s a great writer, and that is not the norm in philosophy. He’s a great stylist, he’s funny, he’s interesting, he’s a bit wicked, he’s rude. And he touches on almost every aspect of human life and he has something to say about it that’s usually somewhat provocative and intriguing. I think that’s the crucial reason why Nietzsche is so popular. Indeed, he’s probably more popular outside academic philosophy because he’s so hostile to the main traditions in Western philosophy.