In reply to the first question, one could probably produce a checklist of symptoms. But in my experience, any such list would be indistinguishable from the litany of complaints of many parents of young adults:

"My son/daughter is irritable, impatient, and intolerant of shortcomings in others. He/she has suddenly become obsessed with his/her particular activity, to the exclusion of all others. He/she is moody, withdrawn, humorless, uncommunicative, and occasionally hostile..."

So the answer to the second question is self-evident: "Yes, the start of the slide is easy to see, but only in hindsight."

I must also emphasise that, in schizophrenia, no two cases are exactly the same, although there are certain characteristics that tend to come to the fore as the disease progresses — a delusion that one is being persecuted or controlled by others, for instance.

Furthermore, I can speak with expertise about only one case: that of my daughter Tessa, whose slide into the abyss started in 1991, when she was 20.

I call it a "slide", but if I had to be more precise I would describe it as a series of steps down. Thus, the first deterioration, in April 1991, was followed by two years of stability, in which she was too concerned about the attitude of others toward her, and too preoccupied with her physical fitness, but still able to perform at close to her potential.

The night of the first deterioration — if, indeed, it can be said to have occurred on a single night — is one I will never forget. Tessa came home before I expected her, to find I had not prepared a meal.

A little annoyance might have been understandable. But she was more than annoyed. She was angry. And the more I tried to make light of my mix-up, the more angry she became — until, in a furious forewarning of the catastrophe to come, she accused me of deliberately failing to cook for her.

The next deterioration, in 1993, was more dramatic, and made me realize, for the first time, that we were in serious trouble, but trouble I almost automatically dismissed as a "passing phase".

Don't all young people flounder a little while trying to find their feet?

Tessa was now 23, and enrolled in a BA course at Auckland University. For a month or so, there seemed to be no reason for concern. She even wrote to us to say she was doing well and was happy.

Then we started to receive interminable telephone calls. People were talking about her. People from the Fitness Foundation in Palmerston North were trying to "ruin/wreck" her life by interfering in her affairs in Auckland. There was "something going on", and she was determined to get to the bottom of it.

We would talk for an hour, as the conversation went round and round in circles. She would voice a suspicion or make an accusation. I would look for something of substance in what she was saying. When I couldn't find anything, I would offer reassurance. Alternately, I would try to reason with her. But nothing I said seemed to make any difference. In fact, she didn't seem to listen.

Eventually, sheer exhaustion would bring the conversation to a close, and I would put the receiver down feeling drained and dazed. And then, the next night, the telephone would ring again...

Taken individually, her complaints often sounded plausible. But when I put them together, there was something wrong with the complete picture. No one could have that much bad luck, I thought.

To put it another way: Things simply didn't add up any more. Two and two no longer made four, or even five, but an incomprehensible 6.389.

Later, I would see that Tessa was no longer amenable to reason because her sense of reality, on which reason is based, was askew. This meant that trying to reason with her was like trying to use a tape measure to weigh a bag of apples.

In May, 1993, she came home for the university vacation. Naturally, I saw this visit as an opportunity for the proverbial "long talk". But strangely, after the marathon telephone conversations, she had little to say. She also seemed uninterested in her studies. I felt uneasy, but was reluctant to "rock the boat" by commenting.

Then, one night, the cataclysm came. There was a cry of alarm from my wife in the kitchen: "Tessa says the people from the Fitness Foundation have been here, and have been spreading rumours about her."

At first, I thought the allegation was a joke. Even if the fitness fanatics were after her, they wouldn't come here, I thought. But it wasn't a joke. A glance at Tessa's grim face confirmed that.

"No one has been here," I said.

"Yes they have. Tell the truth!"

"We are telling the truth. No one has been here."

"You're both liars!"

And so it went on, until we all ended up, about half an hour later, in Tessa's bedroom. My wife was on her knees, sobbing. "I don't know what I've done to you in the past, but please forgive me," she was pleading.

I was enraged. A delusional daughter was bad enough. A distraught mother denouncing herself for imaginary misdeeds was intolerable. This was not Beijing, 1967.

Meanwhile, Tessa sat at her desk, totally unemotional. Occasionally, she would suggest, icily, that her mother cut out the theatrics — and confess. The matter could be cleared up if she simply told the truth.

I think it was this composure that prevented me from realising, until late in 1994, that Tessa was unwell, rather than outrageously cantankerous. For nearly two years, I supposed she would someday see the absurdity of her suspicions, and would slowly return to her former happy, carefree self. And indeed, there were days when she appeared to have "bottomed out", and to have begun to climb back up.

Later, some of the mental health people were also taken in by Tessa's apparent self-possession. "They were impressed by me," she said recently, referring to the crisis team to which I turned for help in early 1995. This was about six months before her final descent into the acute phase of schizophrenia.

Apparently, she presented herself as a capable, optimistic person pursued by uptight parents who "over-reacted" to every trivial upset.

One mental health worker snidely suggested to me in September 1995 — only weeks before Tessa was virtually incapacitated by her illness — that I, not she, had the problem.

He wanted to know what kind of "outcome" I envisaged.

I said I thought Tessa would eventually return to Palmerston North, live in a two-bedroom flat, keep a cat...

He cut me off. "Would that ease your anxiety?" he asked — as though easing my "anxiety" were the ultimate objective of the exercise.

I wish the crisis team could have seen Tessa at the end of the year, as a deeply psychotic patient on the psychiatric ward of a public hospital.

Her persecutory delusions were finally making life almost impossible for her. She was refusing to eat the hospital food, because she thought it was either drugged or poisoned, and was sitting up in bed at night with the light on, because she thought the night nurse would murder her is she dropped her guard.

She also had hallucinations, and a range of crippling psychosomatic disorders brought on by panic attacks.

Ironically, she fled from the hospital five days after she was committed, took a taxi to a nearby town, checked into a motel, and made an appointment with a local doctor.

She was walking down the street to consult him on her "heart condition" when she was picked up by the police.

Told she was being taken back to hospital, she pleaded: "Don't take me back to hospital! They're killing me there!"

Meanwhile, she called me incessantly — sometimes several times an hour — only to hang up after listening to the recorded message on my answerphone, which she was convinced I used to encode secret messages. Even the most innocuous statement had a sub-text, to be extracted by means of assiduous analysis of tone of voice, pace of delivery, and choice of adjectives. In her nighmare world, nothing was as it seemed to be on the surface.

She stopped reading books, because she thought other people could hear the words as she read them.

She also stopped watching television, because she thought the newsreaders and actors knew her, and spoke directly to her. And of course, the people in the street knew her, too, and constantly made unkind and cutting comments about her, referring to her as "it".

In the end, there was safety only in solitude, in a small room, with the curtains drawn.

 FOOTNOTE: Since receiving treatment, Tessa has made a good recovery. Her sense of humour has returned, and she now laughs as she recalls some of the things she did when she was unwell. She is living and working in Palmerston North, saving up for a two-bedroom home unit, and looking forward to keeping a cat...