Every era has its own way of interpreting mental illness. Over the centuries, humanity has created explanations such as demonic possession and its reverse, visionary sainthood; sub-human facial structure and "bedlam"; then immorality, sexual promiscuity and disease. In Ireland in the last century, women were sometimes put into psychiatric hospitals or Magdalen laundries for being, allegedly, sexually uninhibited.

Sigmund Freud offered repressed sexual desire and the subconscious as the enlightened approach. Carl Jung turned to the "collective unconscious" and, with Freud, spawned the growth of intensive talking therapy, through psychoanalysis. R.D. Laing blamed overemotional mothers for schizophrenia.

Most of these theories have been debunked and others re-evaluated. Even Freud, venerated in the last century, is being reassessed.

We still don't have the complete answer, but the biological explanation dominates. The brains of people with schizophrenia appear organically different on MRI scans, for example, and the illness responds well to drugs. Severe depression is linked to the brain's inability to access serotonin, a neurotransmitter. Antidepressants can be lifesavers for people. Current thinking is that manic depression is caused by a chemical imbalance, which can be corrected with the careful use of drugs. But if Beethoven had been diagnosed as suffering from manic depression and given lithium, would he have experienced the storms of creative genius that resulted in his great symphonies? Would Kurt Cobain have captured the pain of a generation if he hadn't been tormented?

On the other hand, would someone such as Janis Joplin, if she hadn't needed to anaesthetise her sensitivity and self-loathing with drugs and alcohol, be alive today? Mental illness is, above all, a part of the spectrum of human experience.

Many people with mental illness are articulate, sensitive and creative. Dr Michael Corry, a psychiatrist, sees them as "the canaries in the coal mine", telling us that the stresses on all of us in the modern world will ultimately be too great.

Corry, who worked at St Brendan's Hospital, in Dublin, in the 1980s, has never accepted the orthodoxy. He suggests that we need to stop seeing people with mental illness as defined by a biological illness and see them as being in the throes of a crisis of the soul.

He believes that many people diagnosed with mental illness are, in fact, hypersensitive spiritual beings who cannot come to terms with human form and seek to return to the "angelic realm" - a spiritual state.

"Fear can drive us mad," he says, arguing that fear forces vulnerable people to escape through psychosis. He doesn't deny that brain chemicals and thought patterns are involved, but he suggests that, in psychosis, people create these phenomena of escape, much as marathon runners become high on endorphins, hormones that stifle pain. He sees the brain as an electromagnetic computer programmed to think in a certain way. Through talking therapy, people can be helped to re-programme the computer.

He still believes the biological aspect has to be acknowledged. He suggests people can create brain chemicals and electrical storms that change the brain organically. This doesn't mean biological treatments should be rejected, he argues.

Drugs are an important therapy, he believes. People in the throes of psychosis due to schizophrenia, for example, need to be stabilised in hospital and brought back to reality with drugs. He is not urging people to give up their medical treatment, although he fears that drugs are sometimes overprescribed, to help people overcome the pain of living.

In a new book, he and Dr ┴ine Tubridy are challenging the helping professions to see mental illness in a spiritual light. Going Mad? Understanding Mental Illness (Newleaf, £8.99 in UK) puts forward the idea that all human beings are spiritual beings having human experiences. The word "psychiatry", for Corry and Tubridy, means soul-healing - psycheis the ancient Greek word for "soul"; iatrieatranslates as "healing".

"Humans are evolving," says Corry. "People will now say to you, 'I didn't want to go there, because it didn't feel right,' or, 'I avoid so and so, because they give me bad vibes.' " He thinks people who experience "altered states", such as schizophrenia, are even more sensitive to "energies" and "vibrations" than the rest of us. They have reached the point at which they find it extremely difficult "to commit themselves to being fully present on the earth plane". Such people may use legal and illegal drugs and alcohol to dampen tortuous feelings of self-loathing and fear.

"As spiritual beings, the human experience for which we have signed up can seem a daunting task," write Corry and Tubridy. "Many of us feel profoundly alienated, with no manual or instruction book for being human. Some of us would prefer not be here because we find the world so toxic and hostile. Those of us who sense that the angelic realm is our true home can feel desolate at such remoteness from our origins, stranded in a harsh place where we must be ever-vigilant of the inhabitants."

Just as former eras have produced explanations for mental illness that reflect the social and intellectual spirit of the age, Corry and Tubridy are reflecting New Age ideas. A huge pop-psychology industry has been created around angels, chakras, vibrational medicine, "past lives" and spiritual healing.

Corry believes interest in these areas is a sign that humanity is becoming more spiritually aware. In the book, he uses case histories to illustrate how people from various interpretative backgrounds see mental illness. A young man is secluded in his bedroom, communing with God. The psychiatrist says the man needs drugs and hospitalisation - a course Corry believes is right in that circumstance. But Corry also agrees with the homeopath, who would use vibrational medicine to adjust the young man's energy fields. A psychologist looks at traumas in his family background, and sees these as contributing to the crisis. A spiritual healer sees the teenager as being "out of sync, out of the space-time continuum", as Corry puts it. While the academic specialist sees the man's brain as being bathed in chemicals and electro-magnetic impulses created by fear.

Corry says he thought long and hard before writing the book, because he wasn't sure society was ready for his ideas. "I was determined to try not to be flaky and take a middle ground," says Corry. He believes the ideas the book promotes are ones that the mainstream medical, psychiatric and psychological professions will have to accept.

"In contrast to squeezing psychological distress into an orthodox pathological framework, it creates more room for the qualities of hope, expansiveness, diversity and interconnectedness. In our view, this is the contemporary meaning of alchemy," the authors write.

"Alchemy is exactly what it is," responds Dr Patricia Casey, professor of psychiatry at Mater-Misericordiae Hospital, in Dublin. She is concerned that Corry's ideas lack scientific proof. Today, when New Age ideas are in fashion, people with mental illness are seen as the "lost tribe", as Corry puts it, of the angelic realm. Casey fears such a view could further stigmatise people with mental illness, because it makes them appear more different than they already are. She wonders if they might feel blamed for being spiritually unable to cope.

"We are not just psychological and spiritual beings, we are also biological beings. That's not to say psychotherapy is not useful for schizophrenia. I think it is deeply stigmatising to people with schizophrenia to say they have chosen to escape from reality or that it's a spiritual crisis . . . It's all very well if you believe science has no merit. Anyone can offer a theory and it can appear plausible. The bottom line is, we have to look at science and what we know and don't know from scientific endeavour."

That's a critical professional view, but how do Corry's clients feel about his approach? The film-maker Martin Duffy has just seen his last film, The Testimony Of Taliesin Jones, win its seventh international prize, this time at the Chicago International Film Festival.

Duffy says Corry helped him to see himself as a spiritual being having a human experience, and so to find the inner peace that had eluded him for so long. "I had been in therapy, for stretches of time over several years, coming to terms with the past," he says. "When I was referred to Michael Corry, I found someone who equipped me for the future. Over the few sessions I had with him last April and May, I came to think of Michael more as a 'mind coach' than a therapist. He taught me a set of skills and opened my eyes to a set of realisations that have transformed how I feel about myself and about life.

"His tool kit consists of everything from homeopathy, mantras and chakra meditations to blunt confrontations about fossilised baggage. Over the four sessions I had with him, he taught me about rituals for breaking free of the past and helped me to awaken inner sources of strength . . . I was accustomed to sitting before a therapist and pouring out my thoughts.

"Michael, however, focused me instead on how life would be starting from now. The dialogue in each session was at best 50-50 - maybe he spoke more than I did. And that is part of the wonder of his approach: he speaks directly from his own clear sense of self and sanity . . . Only since my sessions with Michael have I begun making clear and conscious choices in my life."

This approach of changing thinking, as a way of stopping emotional pain, is not unique to Corry and Tubridy. It's the core of behavioural therapy, and it's latest manifestation, "brief therapy", which finds solutions to emotional dilemmas by altering the way you think. What's different about Corry and Tubridy's ideas is the spiritual dimension. "Flaky" or not, it's an approach that many people, in the "New Age", seem to be hungering for.