The accident, as doctors prefer to call it - they don't like the word stroke - occurred on Thursday July 30 1991, shortly before nine. John got up without waking me, which was unusual. When I reached the kitchen I could see that he had eaten his usual breakfast - muesli, toast with marmalade, coffee. He had also emptied the dishwasher, the one domestic task he enjoyed. But the contents were scattered all over the kitchen: plates, mugs, forks, cups, pots, all jumbled up on the kitchen table.

I heard the crash a few minutes later. It sounded like a heavy picture falling off the wall. He was lying on the floor of his study, next to the desk where he planned to spend the morning writing. His eyes were open and his smile allowed me to believe, just for a moment, that this might be the opening scene of one of his more histrionic practical jokes: like the time when he cured me of hiccups by fusing all the lights in the house we had rented in California and climbing up a drainpipe wearing my long, black evening cape. The neighbours, who noticed him peering into a bedroom window hissing, I'm coming to get you, called the police.

But this smile was empty, with none of John's mischief or irony behind it. It was the sweet, witless smile of a baby. He opened his mouth and said, in a weak but otherwise normal voice: The Walls.

The ambulance arrived 45 minutes later. John smiled at me like an adoring child and stroked my arm with his left hand, saying The Walls over and over in a reassuring voice. In accident and emergency, one of the doctors told me that my husband had suffered a "cerebral vascular accident" - a stroke. There was nothing to be done except provide him with rest and reassurance.

John lay on a trolley for hours, visited occasionally by doctors. Eventually a hospital porter arrived. He wheeled John's trolley into a concrete building, into a lift that smelled of urine and stale cigarettes, up to a ward on the fifth floor. It was the closest place to hell I'd ever been in all my privileged, overprotected, trusting life.

August 3, late afternoon

The ward is very hot. At this time of day the sun glares straight in through the greasy plate-glass window and cooks up an almighty stink - the dinner trolley, unwashed bodies, stale urine. The shade rolled up at the top of the window is stuck - nobody can remember when it was possible to pull it down. The window is also permanently sealed - to prevent suicides apparently. The nurses have explained that the tube and the needles are keeping him alive. But there is never a nurse available when the tube blocks or the bottles are empty.

August 4

Now that he is more alert he is very preoccupied by the problem of not wetting his bed. He is not incontinent but because the nurses have no time to take away full urine bottles he often has no choice but to pee in his bed. So every day before I leave I have to sneak into the supply room and steal three cardboard urine bottles, which he secretes under the bedclothes for use during the night.

August 9

At two this afternoon, when John was sleeping and I was reading in the reception area, a man came up and said, I gather you wanted to see me. He had a fixed social smile on his face and was rocking back and forth on his feet as though judging how to swing a golf club. This was Dr X! - at last, the consultant who was supposed to be in charge of John. He said that a first reading of the CT scan had proved what "everybody here" had known from the beginning. John's case was hopeless. Dr X was not prepared to accept him in the hospital's rehabilitation programme. It would be a waste of limited resources. He suggested I put John in a home. After all, he said, you're still relatively young. You don't want to spend the rest of your life tied to an infarct. I've looked up this word. It means a region of dead tissue caused by a blocked artery.

August 11

I don't trust Dr X. To be honest, I hate him. All I know now is that I must get John out of here. I spent yesterday and this morning on the telephone. The Stroke Association will supply a list of stroke rehabilitation units but will provide no personal advice. The Wolfson Centre at Atkinson Morley's hospital categorically refuses to take any NHS stroke patient over the age of 65, however active their lives before the stroke. They will, however, be happy to accept John in their private branch, which is more than anyone who is not insured or very rich could afford for more than a few weeks.

August 12

The speech therapist is a pretty Scottish lass wearing a floaty summer dress and sandals with very high heels. I told her that John can read and can understand absolutely everything said to him and she said, I wouldn't be so sure. She put four objects on John's bed tray: a razor, a clock, a pencil and some keys. Then she spoke each word very clearly and asked him to point to the correct object. It was obvious he hadn't a clue what she wanted him to do or how he could do it. Then she wrote the words on separate labels and asked John to match them to the objects. Once again, John was stumped. I panicked. If John can't match the simplest of words to the most ordinary of everyday objects does it mean he has less language than a trained ape?

The speech therapist said that although John appears to understand us he is in fact only guessing from clues given by our gestures and tone of voice. As for his reading, he is turning the pages out of what she calls habitual behaviour. I had to admit that he does not persist with the books I bring him. On the other hand, he really does seem to understand his academic journals. I can tell this because he marks them in what seem like appropriate places and answers questions about them by pointing to relevant passages. And he has been reading the newspapers I bring him. They are full of photographs of Serbian death camps. I feel guilty that I am not more bothered by the terrible things happening in other parts of the world. The speech therapist admitted that she had heard a theory that reading for pleasure and reading for information might be two dissociated functions.

August 14

When I came into the ward yesterday morning, John was sitting in his chair, bent over double and moaning, clutching his paralysed leg. I've never seen him show such pain. I found a nurse who said she couldn't give him a strong enough painkiller because addictive drugs are kept in a locked cupboard on another floor of the hospital. Dr X would be doing a ward round this morning. Maybe I could catch him then. I came in at six. Dr X arrived at eight. An hour later he reached John's bed. I asked what might be causing J's pain. Oh, you never know with infarcts, said Dr X. They fall downstairs. But how could he fall downstairs when he can't even get out of bed? Dr X beamed his social smile at me and began to shout: I gave you a whole hour of my time on Sunday and that's as much as you're going to get. I told you that your husband isn't going to receive special treatment. If you go on making fusses he'll suffer for it. Shortly afterwards, two nurses arrived with the painkiller.

August 16

Everything I read about stroke and everyone I talk to who knows about it says that it is crucial that the affected limbs be exercised, passively if necessary. If not, the muscles may be permanently cramped and never recover. I remembered that a neighbour once told me she used to be a physiotherapist. I knocked on her door and to my surprise she agreed to come with me to the hospital. She showed me how to bend and straighten and stretch his right arm and leg. Then she got him into his chair and told him to try to push himself up, not only with his left hand but also with his paralysed one which she held in place on the right arm of the chair. John stood up! It was so unexpected that the three of us started laughing. Then five nurses led by the sister came running in. The sister shoved John back into his chair saying that physiotherapy was not allowed on the ward because the hospital was not insured for it.

August 24

Sometimes The Walls sounds more like The Wars, or more often a cross between the two: The Woahs. I tell her that as a historian John was interested both in war and in walls. She said nobody knows whether these recurrent utterances represent real words, perhaps something the patient was thinking about just before the accident, or whether they are just a sound that is easy to make.

September 1

I've finally managed to have John transferred to an equally underfunded but much better hospital. Supper in the geriatric ward is served at 5pm. The friends start arriving at about 6.30pm, with their news, love problems, gossip. One evening I found John with the curator of prints and drawings at the British Museum, which had kindly kept John on as a trustee, the two of them bent over facsimiles of two prints by Pietro da Cortona, discussing which one the museum should buy. John was saying Da woahs, da woahs, woahs da woahs, the curator replying, Yes, Sir John, I entirely agree that the area around the bridge is damaged but the quality of the rest is superb.

We have become more and more fascinated by the uncanny paradoxes of John's mysterious condition. After an initial success with (writing the word) fork he has not written another real word. But if you gave him a pencil and pad he would grasp the pencil in his left hand and write purposefully, evidently certain of his message, in strings of letters, each string obeying the rules of English orthography, each grouped into punctuated sentences. If I asked him to write something for me he would cheat by fleshing out his text with phrases copied from a newspaper or book. He filled entire notebooks like this: An da rodor wesh rof; rand brinste trab. Refugees from the former Yugoslavia. Blook cridder was droosed.

But John can now read well enough to help with the proof- reading of The Civilization of Europe in the Renaissance. David Chambers, a professional historian who had been one of John's early students at Oxford, agreed to see the book through the press, but only on condition that John should approve each stage of the editing. This was generous, because John could certainly not work with his former precision and speed. His concentration wavered. He spotted some errors and infelicities but missed most. What he could unfailingly do was to tell David where to locate any references he needed to check. He did this by pointing to the location of a library on a map of London, or by drawing detailed plans of his library at home.

October

One evening I was alone with John, facing him across the bedside locker on which I had laid out the supper I had cooked at home and warmed up in the hospital microwave. Supper, in our previous life, had been our favourite occasion of the day, the time when we exchanged the thoughts we had been saving up all day like Christmas presents. I watched John preparing to enjoy his food and my company, and listened to his voice - da woahs, da woahs, da woahs? - asking me to talk to him, tell him about my day. Suddenly I was tired, too tired to carry the burden of a one-sided conversation. I thought about all the unmarried women I knew who said they preferred the company of their pets to having a man around: animals, they say, understand more than you think; they whine and purr and bark when you tell them your problems; some dogs even howl in tune to music. I was too weak to resist a quick, forbidden glance into the future. And what I saw there was a succession of meals, sitting across a table from a husband who was no more, or less, companionable than an affectionate dog.

A doctor I met explained that John was enjoying a condition described by the French 19th-century neurologist Jean Martin Charcot as la belle indifférence , the sublime indifference that can accompany mental imbalance. He was mistaken. Although I was too distracted by self-pity to notice it, John had woken from the euphoric trance that can indeed follow severe stroke. He hid his despair from me until one afternoon when I came into the ward earlier than usual and saw him before he saw me. His stillness and the angle of his neck told me what he would never have revealed in my presence. He was sitting in his chair, his head was bowed, his face covered with his left hand. There was an atmosphere around him of extreme concentration I recognised from his writing days. He was thinking hard, trying to think his way out of his dilemma, and he needed no words to tell me that the only solution he could find was suicide. When I put my arms around him, I felt the tears on his face. He was crying for the first time since I had known him.

He pushed me away. He opened his mouth and pulled at his tongue and lips. He grabbed a pencil and scribbled violently in the air then threw it on the floor. He mimed himself as an idiot, head lolling, eyes rolling. He began to talk in his wordless voice. I listened and realised what he was saying. With a phonetic range more restricted than a baby's, he spoke to me by modulating his voice: its pitch, rhythms, timbre, timing, intensities as eloquent as ever.

I reminded him that he had always believed suicide to be the most disgusting and unjustifiable of acts, as immoral as murder. Nobody, he used to say, owned their own life; it belonged to all the people affected by that life. I needed him now more than I ever had. He banged his fist on the bedside locker with a resounding WOAHS. It meant: OK then. You win. Let's have a go and see what happens.

1992

When John came home at Easter, nine months after the stroke, I was surprised by how quickly our life resumed its normal rhythms. With the help of a group of friends and two therapists we continued the search for his lost language. The race was on to see who would be the first to conjure forth a word from John.

It came on a rainy afternoon in July, almost a year after the stroke. John and I were sitting by the fire in Camilla's drawing-room. John was looking through his collection of postcards of Old Master and modern paintings, amassed over many years of travel. He paused at a picture of a young woman seated behind a table where she is tuning a stringed instrument. Her face and eyes are turned away towards the window on her right, which lights the yellow sleeve of her dress and the pearl earring dangling from her left ear. A map of Europe hangs on the wall behind.

John stabbed his index finger over and over at the postcard, accompanying the gesture with the emphatic grunting noises that he made when something moved or excited him. He raised his left hand and drew a sign in the air that looked like the letter V. I found a pencil and paper. He wrote V-e-r. I yelled for Camilla. She arrived just in time to witness the completion of the miracle: m-e-e-r: Vermeer!

In the next days and weeks, the picture side of postcards prompted more artists' names. He wasn't allowed to cheat by turning the postcards over, and he had no need to. The names he wrote were not always perfectly spelled, but it was clear that he knew them, and the obscure names came to him as easily as the most famous. They started as, for example, H Bosck, H Mamlenb, Georg Faedrick Kerstong, Wichilengolo. Although I thought this was good enough, John recognised that they were not right and painstakingly corrected each one, over and over, letter by letter, until he got it right: H Bosch, H Memling, Georg Friedrich Kersting, Michelangelo. But he could not even make a guess at words like chair, cup, cat, or even Sheila.

How could this be possible? As I began to read more about aphasia I came to understand that language, the awesome intellectual skill we acquire without the slightest effort by the age of three and grow up taking entirely for granted, is one of the great scientific mysteries. It is also more vulnerable than most of us suppose. Gradually, over the next six years, John regained the ability to read for pleasure and to write meaningful sentences. But he never managed to speak more than a handful of words.

On the morning of August 12 1999 John died peacefully in his sleep next to me in bed. We gave thanks for his life on a relentlessly beautiful morning, with the sun shining on his coffin through the high leaded windows of our local 18th-century church by the river. Bamber Gascoigne, my oldest English friend, gave the address. He spoke of the acclaim John would have received if he had died after his stroke in 1992: "But John didn't die in 1992. He lived on to see The Civilization of Europe in the Renaissance win prizes and international acclaim. But more important than all that, he survived to build a new life at least as impressive in its own way as his previous one. Surely no one else has spent seven years as a fully active mind, trapped in a cage of silence, without ever lapsing into bitterness and resentment. That was John's final achievement. It should serve as an encouragement to others with the affliction of aphasia."

If I were to start writing about John's aphasia today it would be a much angrier book. When John had his stroke in 1992, I was innocent of all thoughts about the larger issues of healthcare provision of old age. One in 20 British "geriatrics" - those over 65, in the NHS - claims that they have at some time been refused treatment because of their age, but the true percentage is likely to be much higher because this generation was brought up not to complain. Educated or not, they tend to have faith, as indeed John did, in professional integrity. If the doctor tells them they will never walk or talk again, they assume that the doctor is telling the truth and doing his/her best.

Looking back now I can see all too clearly that John survived his stroke and lived on to contribute so much only because he was extremely fortunate. He was blessed with a robust temperament and constitution, a large circle of loyal friends and family, and a wife still young enough to fight for his life. Without so much resilience and support he would probably have died, as thousands of stroke victims do each year, of neglect.

· The Man Who Lost his Language by Sheila Hale is published today by Allen Lane, priced £14.99. © Sheila Hale, 2002.