Motor neurone disease has left the historian Tony Judt quadriplegic and, he tells Ed Pilkington, has forced him to think about what it really means to be human. The result is an astonishing series of essays and a determination to get young people thinking collectively again

A few weeks ago the English historian Tony Judt delivered a speech at his home in New York University (NYU). More than 1,000 people turned up, and few left disappointed. What they heard was classic Tony Judt: the lecture, a plea for the positive virtues of social democracy, was as erudite as might be expected from the author of Postwar, his epic portrait of Europe since 1945, and as politically pointed as his controversial writings on the Middle East.

The Judt they saw that night, however, was anything but expected. He rolled on to the stage in an electric wheelchair, a blanket wrapped around his body so that all could be seen was his neck and head, to which a breathing tube was attached like a bit of facial Tupperware. "The last time anyone had seen me in public I'd been bouncing around the stage full of fitness and energy," Judt says. "Now they saw this quadriplegic with plastic on his face."

He was concerned about how his audience would react to the new-look him, and tried hard to make them feel at ease. It worked, and at the end of the speech he received a standing ovation.

It was only afterwards that Judt suffered the intense irritation of being accosted by someone who seemed unaware of the difference between physical and mental incapacity. "I'd just delivered this long lecture completely by memory, no notes, for an hour and 15 minutes. Someone comes up to me and says 'TTTTOOOOOONNNNYYYYY. DOOOOOO YOOUUUUUU REMEEEEMMMMBER MEEEE?'" Judt mimics the person in an exaggerated drawl, as though he were talking to a baby in a buggy. "I thought, 'You stupid bitch! Of course I remember you. I know your name, I know where you teach, I know everything about you!'"

Tony Judt may have lost the use of his arms and legs, but he has lost none of his feistiness.

We are sitting in his book-lined study in a NYU apartment off Washington Square. The room is swelteringly hot, for reasons that only become clear later. Judt is sitting in the electric wheelchair, dressed in a black T-shirt and loose trousers. He has that plastic tube attached to his face as well as a microphone, which amplifies his voice through a speaker on the book shelf.

Eighteen months ago Judt was, by his own description, "a 61-year-old, very healthy, very fit, very independent, travelling sports-playing guy". He had a slight shortness of breath walking up hills and found himself hitting the wrong keys when he typed, nothing more.

Then in September 2008 he was diagnosed with motor neurone disease, a progressive degenerative illness that causes the cells which control movement to die. His specific condition is amyotrophic lateral sclerosis (ALS), known as Lou Gehrig's disease after the legendary New York Yankees hitter who died of it in 1941.

The disease ravaged Judt with astonishing speed. By December he had lost the use of his hands. By March he was in a wheelchair. By May he was wearing the "silly-looking facial tubing" as he puts it, because his diaphragm muscles were no longer strong enough to effect the bellows motion that induces breathing.

He gives me a little display. "So I want to move my right arm but nothing happens," he says, with the only visible sign a slight flexing of his right bicep. Then he tries to move his legs and I can see a tiny spasm in both thighs.

"The leg you will see twitching and that's about it. That takes a huge amount of effort because from the body's point of view it's as if I've just kicked my leg up five times."

The suddenness of the catastrophe would leave many people paralysed not just physically but emotionally. Judt has responded differently. He has embarked on a fascinating, albeit involuntary, intellectual journey – a forced march of the mind.

"I was forced to think very hard about what it meant to be me, what it means to be a person who is only a brain. Pascal's 'thinking reed' really does capture it, because I'm just a bunch of dead muscles thinking."

So what does he think about? "I find myself thinking about what is the core me-ness in me. What's the core places, influences, events, pleasures or angers, turning points and so on. I'm trying to work out what it must mean now to be reduced to the essence of who I am."

The product of this existential delving is a series of essays that Judt has written – or rather dictated – for the New York Review of Books (NYRB) that will be published over the next three months. One tackles his illness head on. In Night, reproduced here, Judt subjects his own deterioration to the same unsparing scrutiny as he would the Israel-Palestine conflict, say. Its absence of any self-pity makes for harrowing reading.

The other eight essays take us back in time to formative aspects of his childhood in England. He was born in 1948 to lower middle-class parents and spent six years living in Putney in south-west London – a location that forms the theme of one of the essays. In others he introduces us to Joe Craddock, his school German teacher, lamenting that Craddock's insistence on excellence ("Yer utterly useless!" he would shout at pupils) is unthinkable in today's pampering education system. He finds meaning in the melange of largely bad food he was served as a child and revels in his love affair with trains that is now deprived him by his immobile condition.

Taken together, the essays illuminate the many contradictions in Judt's make-up that give him such a distinctive voice. He is a Jew with no religion who has questioned the legitimacy of the state of Israel; a naturalised American citizen who is a consistent critic of overweening US power; a person of the left who subscribes to no leftist ideology.

He is, to use a phrase that Judt applied to Edward Said, a rootless cosmopolitan. "Today I'm regarded outside New York University as a looney tunes leftie self-hating Jewish communist; inside the university I'm regarded as a typical old-fashioned white male liberal elitist. I like that. I'm on the edge of both, it makes me feel comfortable."

One of the NYRB essays, Kibbutz, explores his fraught relationship with Israel. Between the ages of 15 to 21 he developed an almost obsessive passion for left-wing Zionism, then fell as abruptly out of love with it. At his parents' suggestion, he spent time on an Israeli kibbutz and embraced its dogma with the zeal of a new convert.

But as he grew older he came to resent its restrictions and dislike its conservative smugness, a feeling that intensified when he spent time with the Israeli armed forces on the Golan Heights just after the six-day war in 1967. The whole experience, he says, immunised him against the unthinking ideology of Zionism, a pattern repeated with regard to Marxism. "I remember going through the 1960s watching my friends become Maoists or Althusserian feminists or God knows what else and thinking, this is garbage. So I became post-ideological."

His non-conformism has come at a price. His stance in favour of a "one-state solution" to the Israel-Palestine conflict – that is, an end to Israel as a explicitly Jewish state – has landed him in hot water, particularly in New York where he has encountered much less intellectual tolerance on this topic than within Israel itself. He remains unflustered by the flak. "I don't have a bad conscience. I know exactly who I am. I'm Jewish. I've never been conflicted about it, never been religious, never embarrassed about it."

He does get flustered, however, by threats made against him and his family. After he wrote a Financial Times article on the Middle East last month he received a letter from Rabbi Kahane – the same name as the violent extremist Zionist who was assassinated in New York in 1990 – saying that Judt was now a "marked man".

His current intellectual preoccupation is with the role of the state in western societies – the subject matter of his NYU lecture. His thesis is that over the past 40 years, western democracies have forgotten the positive virtues of collective action. "What has gone catastrophically wrong in England and the States is that for 30 years we've lost the ability to talk about the state in positive terms," he says. "We've raised a generation or two of young people who don't think to ask, what can the state do that is good?"

At the end of the lecture he was struck by how many young people came up to him expressing amazement at ideas they had never heard before. "This is the second generation of people who can't imagine change except in their own lives, who have no sense of social collective public goods or services, who are just isolated individuals desperately striving to better themselves above everybody else."

Judt now intends, in the time he has left, to devote himself to writing a book to help young people think collectively again. "It could really have an impact if I get it right. Something that will get the next generation to see there is a way to think about politics that is not just the way we've been habituated to do it. I care about that and I think I can do it."

Judt is already working on the book, using the same memory technique that he deployed for his NYRB essays. During the night he builds in his mind a Chinese memory palace – or in his case a modest Swiss house – and into each of its rooms he imagines placing a paragraph or theme of the piece he is composing. The next day he recalls each room in sequence, unloading its contents by dictating it to his assistant.

Some people have tried to comfort him with the thought that such mental discipline renders Judt's condition bearable. How wrong they are. "There have been people who have said to me, 'Tony, you are so lucky. More than anyone you live the life of the mind. It could have been so much worse.'"

To which he replies: "Hello! Are you from Planet Zurg? This is one of the worst diseases on Earth. It is like being in a prison which is shrinking by six inches each day."

It is true that he has exceptional mental strength. Against that, there are torments that come with this disease. An intensely independent and proudly autonomous man, he can now never, not for a second, be left alone.

The overriding truth, he says, is that "this is just hell. Because there is no hope, no help, and you know what the ending is going to be, each day is going to be like the last day only maybe a little bit worse. Sisyphus-like, you are going to have to roll this bloody rock up the hill tomorrow in exactly the same way."

We've been talking now for more than an hour, and Judt asks his assistant to move his legs and arms into a new position. He lets out a faint groan of relief. Being motionless for so long, his body hurts; it also grows cold from lack of blood circulation, which explains the sweltering heat in the room.

His ALS has come upon him so swiftly that, under usual expectations, he would be dead within months. But the degeneration of his upper motor neurones, which control his head and voice, appears to be occurring very slowly, raising the hope – or is it fear? – that he may stay as he is for quite a while. Inevitably, though, he will lose all power of communication, bar the ability to wink.

So does he think of euthanasia, of putting an end to an existence that he calls "cumulatively intolerable"?

"There are times when I say to myself, this is so damn miserable I wish I was dead, in an objective sense of I wish I didn't have to get up this morning and do it all over again. I've thought about euthanasia a lot, not for tomorrow, but one has to plan for it because the likely trajectory is that you lose your capacity to express yourself long before you die.

"No one wants to live in a wheelchair unable to talk, only winking once for yes and twice for no. It's perfectly reasonable that there will come a point where the balance of judgment of life over death swings the other way." At that point, he says: "The biggest thing to take into account is not your own feelings but your family's."

All that lies ahead. For now though there is the daily rock to be rolled up the hill, the Swedish house to be filled with night-time compositions, the book to be completed. Tony Judt is in hell. But he's by no means yet defeated.