Adam Phillips writes in the same room in which he practises psychoanalysis. It is book-lined, bright and airy, cluttered but in a way that seems necessary and ordered rather than neurotic and self-defeating. It is, in fact, exactly the kind of room one would imagine a psychoanalyst would write and practise in. It feels odd then, to be sitting on his leather couch, while he sits in the chair opposite, and to begin an interaction that is in many ways the antithesis of the interactions that usually take place in this room.

I am here to interrogate Phillips about his new book, Going Sane. He seems eager to get down to business and there is something about him, a kind of polite intensity, which suggests that small talk, an often productive preliminary to a revealing interview - though perhaps not to a successful therapy session - is not an option. So we jump immediately into madness. Although Phillips's book is essentially about the notion of sanity - what it means, how it might be measured, whether it can be attained and indeed sustained - it is difficult, as he points out, to talk about one without the other.

'Sanity does not immediately strike us as a fascinating idea the way madness does,' he says, leaning forward in his chair, his eyes closing in concentration as they will throughout our conversation, 'even as an alternative word to mad, sane is so blank. But, it seems to me that either madness is another word for human nature, and that we are all very strange and life is, as it were, maddening, or, we are capable of actually being something else. Now, what is that something else? That is what I am trying to explore and I think that it is actually very obscure, and neglected.'

This would indeed seem to be the case. While there have been countless books written about madness, sanity has, until now, been an intriguingly overlooked subject, untouched by Shakespeare, Freud, Blake or Jung, and all but ignored by the self-appointed gurus of the self-help industry. This suggests to me that we take our sanity for granted, that only when it is dramatically ruptured - by grief, depression, breakdown - do we think about it at all. Like Bill Wyman's famous definition of a great bass player - you would only realise how good he was if he were to stop playing mid-song - sanity is defined mainly though its absence. And, while we have invested certain kinds of madness with a kind of romantic allure - the tortured genius of Sylvia Plath, the creative madness of Artaud or Van Gogh - sanity, as Phillips acknowledges early on in the book, has never been fashionable. Or, as he puts it, 'Sanity has always been an unfashionable term that has never quite gone out of fashion.'

To look at what it means to be sane, says Phillips, hinting at perhaps the key subtext of all his writing, 'is another way of looking at what are our hopes for ourselves.' Indeed, if you were to approach all his 11 books as a kind of loosely unified project, which he insists they are not, you could quite easily call that project Another Way of Looking at What Are Our Hopes For Ourselves.

In the past, Phillips has made us think in a new way about, among other things, boredom, flirtation, clutter, monogamy, escape, death, and daydreams. His first book was called On Kissing, Tickling and Being Bored, and it set the tone for what was to follow, being both as playful as its title suggested, but also intellectually rigorous and, in its questioning of the claims made on behalf of therapy, sometimes startling. He may well be the most sceptical psychoanalysts practising today, and has famously said that, 'for me, psychoanalysis is only one among many things you might do if you're feeling unwell - you might also try aromatherapy, knitting, hang-gliding. There are lots of things you can do with your distress. I don't believe psychoanalysis is the best thing you can do, even if I value it a great deal.'

Like all Phillips's work, Going Sane dances around the notion that what we think we want may not be what we really need - may, in fact, be distracting and diminishing. Thus, he explores the madness of money and the madness of sex, two of the peculiar but not exclusive obsessions of the emotionally out-of-kilter times we live in, though not, interestingly, the madness of celebrity or the madness of reality TV, two recent cultural phenomenons that suggest we are being driven to distraction by the relentless inanity of our distractions.

Celebrity, and its discontents, he says, is 'a whole other subject', and one he may yet get around to analysing. That there is such a thing as 'celebrity culture' - an oxymoron if ever there was one - and that it can make people feel inadequate, or envious, or fuel an addiction to binge-shopping or Botox, seems to suggest that every culture gets the madnesses it deserves.

'Yes, that seems to be true. When psychoanalysis started, for instance, it was mainly dealing with sexual inhibition. By the Fifties, it was primarily about identity - people not knowing who they were and believing that they should know who they were. Now, people like me are seeing more and more people who feel a kind of despair about the pointlessness of their lives, or an impossibility about sexual relationships. Or, they feel a generalised phobia, an anxiety about so-called ordinary things.'

This difficulty we have with accepting ourselves, says Phillips, is compounded by the fact that we live in an intensely competitive, market-driven culture that offers us increasingly unrealistic models of a better life. 'If you are told that there is nothing to achieve in life beyond material success,' continues Phillips, 'you are already being given such a narrow, cliched picture of what a good life is. Likewise, if you are presented with celebrity as the ultimate model of what a better life might be, you are being sold a very basic and superficial version of a better life. The notion of a good life could not be more diminished than it currently is.'

One of the best things we could do as individuals, Phillips tells me, is 'allow ourselves to daydream more'. In this belief, of course, he is in direct conflict with the thrust of our culture, which is geared to ever more activity: longer hours, more multitasking, always the need to be keeping up, or running at full pelt to try and catch up. 'One of the more distracting things about capitalist culture,' he says, with total seriousness, 'is that there is no stupor, no time to vegetate. What I would suggest is more time wasting, less stimulation. We need time to lie fallow like we did in childhood, so we can recuperate. Rather than be constantly told what you want and be pressurised to go after it, I think we would benefit greatly from spells of vaguely restless boredom in which desire can crystallise.' This will please my slacker friends immensely, but it also appears to me, the more I think about it, to be an obvious truth. And one that seems radical in the context of our fast-forward society.

It seems to be dawning on us, too, that, though our lives are easier - that is to say, less poor, less threatened by disease and death, less prescribed by class, gender or race - than our parents', or our grandparents', lives, they are nevertheless more pointlessly complex and, as a result, we seem to be more unhappy. That unhappiness increasingly manifests itself, as Phillips's patients illustrate, in a strange dissatisfaction with ourselves, and in our inability to be, for want of a better word, contented. It struck me, while reading his new book, that the ability to be contented may be the key determinant of the sane life he outlines in the final chapter.

'It certainly seems to me that we have unrealistic expectations,' he says, 'Of our relationships, about happiness, about hope. We are not educated to love reality. It is very difficult, for instance, to accept people as they are. One of the most difficult things is to acknowledge our parents as people, to accept that there are not better parents inside our parents.'

Going Sane differs from his previous books in one crucial way: it culminates with a chapter that is the closest he has yet come to offering a prescription for contentment. It is, unsurprisingly, a complex prescription, a series of negotiations between what is possible and what is practical, what we want and what we might be prepared to settle for. I ask him, out of personal interest, how a sane relationship might work.

'Well, first you would not be preoccupied by whether it was working or not. You would be preoccupied by whether or not you enjoy or crave each other's company. So, it would not be working the way a business works. That would be exactly the wrong model.'

What, though, would be the right model? 'Well, it may be in time that we come to see friendship as our best picture of a working relationship. It may be, too, that we need accept that sexual relationships are inevitably unpredictable. One would not then measure the success of a relationship by how long it lasted.

Whether a relationship works for 20 years or for 20 days is not the question The question is, is my life better with this person? And better, in this instance, does not mean more glamorous or richer or more alluring, there is more to it than that.'

With Adam Phillips, one feels, there is always more to it than that. One of the first things you notice about his writing is that he takes nothing for granted about his subject. He is suspicious of received wisdom and sceptical of authority, even his own. He once said he hated the 'intrusiveness' of psychoanalysis, that 'most people are essentially private and the demand to articulate oneself is quite often a strain, and, in the process, can be a diminishment'. His writing, you feel, is a self-interrogation as much as anything, a way of keeping himself alert to the risks and pitfalls inherent in his other profession.

'Writing,' he says, 'is how I work stuff out and even the response is part of that.' The response so far has been overwhelmingly positive. Interestingly, the few dissenting voices have tended to be female and proscriptive: Carmen Callil dismissed Monogamy, his small book of aphorisms on relationships, as 'self-interested and uninteresting', while Elaine Showalter attacked Equals, his exploration of equality in relationships, for its 'stylish one-upmanship' and lack of humour, clarity and a personal voice'. For his devotees, though, the personal voice rings loud and clear and, if at times, his work reads as if he is thinking out loud, that too is part of its democratic tone. 'I just write these books for the people who love them and hate them. If people are taken by them in some way, or can use them, I am thrilled by that, but there is no massive project here to convert people.'

Phillips was born in Cardiff in 1954 and is an only child. His parents were second-generation Polish Jews, and his childhood was relatively uneventful, as much as a childhood can ever be. 'No one divorced,' he says; 'No one died.' He grew up as part of an extended family of aunts, uncles and cousins, and his parents were 'very consciously Jewish but not believing'. His father was the first of his family to attend university, winning a scholarship to Oxford, where his parents insisted he studied law rather than English literature.

As a child, Phillips's passion was nature and the study of tropical birds in particular, and his deep and abiding love of literature did not begin until adolescence. He read English at Oxford and his defining influences are literary.

To this end, he has edited a book of Charles Lamb's prose and co-written a critical study of John Clare's poetry, as well as being the general editor of the recent Penguin Modern Classics Freud translations. He considers Freud to be first and foremost 'a great writer', and 'greatly admires the likes of Carlyle, Arnold and Ruskin - people who wrote as well as they could about the things that mattered to them'. This, as he is well aware, is a perfect description of his own writing, as well as a clue to how he would like the world to see him.

As befits someone whose other profession is bound by an unspoken vow of secrecy, Phillips is guarded about his private life, though he did have a long relationship with Jacqueline Rose, professor of English literature at Queen Mary's College, London, and something of a fellow traveller in the field of psychoanalytical essay writing. They have an adopted daughter, Mia, brought over from China as a baby. Nowadays, apparently, he lives with Judith Clark, a curator at the V&A.

Now 50, Phillips looks much younger and has the tousled, lived-in look of someone who came of age in the freewheeling Sixties. His writing, too, sometimes has the playfulness and disrespect for authority, as well as the utopian undertow of that altogether less uptight decade. 'I believe more in the Sixties now than I did then,' he says. 'All those values that have been mocked and disparaged seem to get truer and better as time goes on.'

His radicalism, which seems to have grown with every book he has written, may be rooted, too, in his experience of the National Health Service, in which he worked for almost 20 years, eventually becoming principal child psychotherapist at London's Charing Cross hospital. There, and in the drop-in centre for maladjusted children he helped set up in Camberwell, he treated people who were worn down and used up by the sheer grind of their lives, for whom therapy was literally a last resort, a place where they could at least offload and be listened to. The experience left him worn out, too, and one suspects that his self-reinvention as a sceptical psychoanalyst and literary iconoclast may be rooted in his disaffection with his profession's unwillingness to test its theories and treatments in the real world where those who need them most seldom have access to them.

In the field of psychoanalysis, then, Phillips is something of a loner, ignored rather than castigated by his fellow professionals for his irreverence and iconoclasm. Since he wrote The Beast in the Nursery in 1998, his books have, to one degree or another, been an ongoing interrogation of his own profession. Over and over, his writing asks us to consider what therapy is for, perhaps because he is acutely aware of how easily it can be misused. Is it, for instance, as that book suggests, 'another spurious form of authority?' Has it become the opposite of what it set out to be, a means of disempowering us, a method of managing our disillusionment and diluting our idealism? Can therapy, as he once put it, 'teach you to bear too much?'

His writing, too, seems to have become more political, though not in any obvious campaigning way. What is striking about the new book is how the symptoms he identifies in his patients - dissatisfaction, despair, hopelessness - reflect the collective anxieties that are abroad right now. What this betokens, among other things, says Phillips, is 'a profound political despair'.

'There does seem to be a loss of confidence in politicians and in the idea of participatory democracy,' he elaborates, 'but there is also a lack of genuinely competing political visions. That, I think, is worrying for our collective well-being. People need an arena where they can think, argue and engage their passions and, perhaps more importantly, they need to feel they are being listened to. That's what politics is for essentially. And that's also what psychoanalysis is for - to speak in order to be able to find out what is on one's mind, what impact that has on others, and what it evokes in them. It is never a good thing to be made to feel helpless.'

Reading Phillips, and indeed listening to him, which is kind of the same thing, is a to be made aware of how carelessly we throw words around. His writing can be difficult and sometimes dense, but it is always thought-provoking. Does he think he has succeeded in getting his ideas across, given the complexity of those ideas and his unwillingness to make them appear less so?

'That's an interesting question,' he replies, looking momentarily perplexed. 'I mean, I don't really think like that. I don't have theories, I have sentences. I don't want people to come away thinking, this is what Phillips thinks about X or Y. My wish is not to inform people, but to evoke things in them by the way the writing works. That, I value. Ideally, I want the books to return you to your own thoughts.' In this, I think, he has succeeded.

· Adam Phillips will appear on ITV's South Bank Show on 27 February