Why is there so much depression about these days? Are there really more depressed people in the world? Should all those dark and gloomy poets - the enfeebled backbone of English literature - just have taken a course of pills and lightened up?

Darian Leader, in his compelling and important new book, suggests we need to redefine depression "as a set of symptoms that derive from complex and always different human stories". He states that "to treat a depression on the same model as, say, an infection requiring antibiotics is always a dangerous decision". Prescription drugs don't speak back to you, nor do they increase your self-knowledge. If you have been divorced three times, taking antidepressants will never show you what you've contributed to this state.

It is unfortunate that "depression" has become as vague a term as "fever", and that far from advancing in our knowledge of our mental states, we are reversing into ignorance. The contemporary refusal to acknowledge unconscious conflicts and a tendency to speak vaguely of "stress" and "genetics" leave us with a reduced vocabulary. What we are suffering from (among other things) is a lack of words and better ideas. Empiricism can only take us so far; it is the hidden - our unreachable secrets, which generate puzzling symptoms - that is doing the damage.

If it is a tempting simplification for the medical profession to believe that the mind is treatable in the same way as the body, this links with Marx's idea that human beings, under capitalism, would become commodities, or "resources". Depression, therefore, may be a kind of social or psychic rebellion or refusal, as hysteria can be, in other circumstances. But resources cannot mourn, nor should they become melancholic, which Leader sees as being one step away from depression, as a deep self-loathing. For the melancholic, who identifies completely with the one he has lost, "It is the core of his being which is unworthy or wrong."

The dead take up residence inside us; it is them we are really berating in our self-reproaches, not ourselves. We have to acknowledge, in speech, how much we have hated our loved ones. This is because they are not dead enough. As we have become less religious we have fewer rituals - public and family ceremonies - for disposing of the haunting dead. As such, if we are depressed it may be because our mourning rituals have shrunk. We can attend the funeral of a parent in the morning and return to work in the afternoon.

And yet, oddly, if it has now become unfashionable for psychoanalysts to deal with death, the dying, and the melancholy that issues from loss, our popular culture is uncannily saturated with it. The repressed has returned. The work of mourning always requires other people. There was the mass sorrow that followed the death of Diana, Princess of Wales. There is the popularity of zombie movies and those featuring ghouls, vampires and numerous varieties of the "undead". And, in literature, we have seen the recent proliferation of "mum and dad" books such as Blake Morrison's superb And When Did You Last See Your Father?. These are attempts to mourn a parent, as well as to ask questions about the nature of catharsis itself and the place of death in contemporary life.

When it comes to the talking therapies, the alternative to antidepressants has become cog nitive behavioural therapy (CBT), which Leader considers to be a form of brainwashing or vacuous positive thinking. Unfortunately CBT, now becoming more widely available on the National Health Service, is considered quick and reasonably cheap. Apart from its conceptual inadequacy, its drawback is that it doesn't work. For Leader, "CBT has no place for the realities of sexuality or violence that lie at the heart of human life."

What then can we do?

Freud never suggested that everyone should have Freudian therapy, though there do exist forms of speaking and listening - of therapeutic conversation - which can be liberating for some people, as they hear the desire of their own unconscious in free association. Freud said there was therapy already for the masses, and it was called culture. Darian Leader observes how, fascinatingly, going to a bookshop to look for non-fictional accounts of mourning and finding none, he realised there was nothing but accounts of mourning in the fiction and poetry sections. The experience of loss and renewal has been central to literature.

An engrossing and wise book, The New Black is not only an illuminating read. It convinces us that this level of intelligence and ideas is essential today, otherwise the general public is left with only the feeblest guides to life, self-help books, "cheer-up" manuals and the fatuous notion that our conflicts are caused by something we can only describe as brain chemistry.

Hanif Kureishi's new novel, "Something To Tell You", will be published on 6 March by Faber & Faber