One summer’s day in 1976, the philosopher Daniel Dennett was driving along the Massachusetts turnpike when he had a disquieting thought. “If somehow my brain were moved into my chest cavity without destroying any connectivity, wouldn’t I still think my mind was right behind my eyes and between my ears?” Perhaps he could be decapitated and still be a professor of philosophy.

By the time he reached Poughkeepsie in New York state, Dennett recalls in his paradoxically engaging and annoying memoir, this thought experiment had become even wilder. What if his brain was kept alive in a vat connected to his body with radio links? Would his mind be in the vat? Bewitched by the possibility, he gave university talks in which he, like some philosophical PT Barnum, would toggle a switch on a metal box with a radio antenna and tried to convince his audience that he was being controlled by his remote brain.

The 1970s was the decade in which nutty professors such as Dennett regularly dreamed up thought experiments to explore the limits of what it is to be human. Thomas Nagel’s 1974 paper What Is It Like to Be a Bat? mused on whether we could still be human if we had bat-like features such as the ability to echolocate. Derek Parfit developed the teletransportation paradox, modelled on Star Trek, by which your molecular composition is sent to Mars, where some gizmo recreates you from local carbon and hydrogen. Is the Martian a replica of you or is it you?

Dennett, similarly, wanted an answer to a question. He wrote a paper with the title Where Am I?, including his brain-in-a-vat hypothesis, which, he tells us proudly here, powerfully influenced the makers of The Matrix. Dennett imagined that we might be brains in vats, while in the film the Wachowski siblings imagined that humans don’t realise they are really living in pods, duped by super-intelligent machines into believing a computerised simulation pumped into their brains is reality.

The location of our thinking selves has bedevilled philosophers ever since, in the 17th century, René Descartes supposed the seat of the soul was the pineal gland. His idea was that the immaterial soul – somehow – controls the gland that in turn moves animal spirits or streams of air from sacs also in the brain. Such, for Descartes, is thinking. Dennett’s tutor at Oxford, Gilbert Ryle, eviscerated this idea. He called the immaterial soul a “ghost in the machine”, a spooky nonphysical entity able to give and receive data to a physical entity – the body. Much of Dennett’s career can be seen as a continuation of the exorcism of that ghost from the machine-like human.

The cute title of the 81-year-old’s memoir echoes his philosophical nemesis Descartes’s insistence that humans are essentially res cogitans or thinking things. But that’s a category error: to be human means to do more than think – at least if you’re doing it right. We are not brains in vats but essentially embodied.

In his 1991 book Consciousness Explained, Dennett railed against what he called the “Cartesian theatre” – the idea that once one junks Descartes’s idea of an immaterial soul that can outlive bodily death, what remains of Descartes’s model of the mind-body relationship involves a tiny in-brain cinema in which, effectively, a homunculus observes sensory data projected on a screen.

But there is no cinema, no screen and no self for Dennett: rather our brains and bodies are machines that process information and the self is not a locatable entity but what he calls “a centre of narrative gravity”, a story we tell ourselves about our experiences. Or rather, stories: we continually revise our narratives about our experiences as more data is processed.

What nonsense, reply his foes. The philosopher Galen Strawson called Dennett’s idea that consciousness can be illusory “the silliest claim ever made”, which, if true, would be quite the achievement. Other critics charge that his book should better be titled Consciousness Explained Away, since it sloughs off what is most important to human experience. Other philosophers have claimed that scientific explanation can never fully account for what is really valuable in human experience. Always waspish, Dennett describes the latter as “mysterians” – that is, people who believe that beyond scientific explanation there are something called “qualia”, namely, introspectively accessible, phenomenal aspects of our mental lives.

Dennett recalls having a drink with a leading defender of these mysterious entities, Wilfrid Sellars. “As we polished off a bottle of chambertin, he said: “Dan, qualia are what make life worth living!’” For mysterians, science can specify the chemical properties of a mouthful of vintage chambertin, but can never know whether my experience of it is qualitatively identical to yours. Dennett, for his part, thinks qualia are as chimerical as immaterial souls. Consciousness exists, he thinks, but not independently of behaviour and dispositions, which can be scientifically studied.

These are deep matters and yet Dennett is an unreliable guide to them. His memoir involves more chippy score-settling with intellectual opponents, some of them long dead, than is dignified. But Dennett is a conceited fellow: it takes someone with an overdeveloped sense of self and an underdeveloped sense of tact to write the following: “The philosopher Don Ross once said of me: ‘Dan believes modesty is only a virtue to be reserved for special occasions.’” My copy is now dotted with marginal “ughs” to register my irritation at some piece of professorial preening. Even when Dennett tells us the truth about himself – namely, that he is one of the few philosophers to get out of the armchair to study neuroscience, artificial intelligence, computer science and psychology – the tone is boastful. He is unremittingly self-hagiographic, confirming the notion that autobiography can be the lowest of literary genres. He transforms an interesting thinker into a dull protagonist.

Dennett is best known today as one of the four horsemen of the atheist apocalypse. Along with Richard Dawkins, Christopher Hitchens and Sam Harris, he argued that God doesn’t exist, that intelligent design is an oxymoron and that faith is a kind of cognitive disability. He once asked an evangelical pastor during a radio interview what if he was wrong about his faith? The pastor replied he had no need to ask such questions: faith trumped reason. Dennett draws the moral: “Right there, I submit, lies one of the greatest dangers to civilisation… religious faith gives people a gold-plated excuse to stop thinking. Anybody who has been persuaded that it is their religious duty not to question their faith has been partially disabled.”

It’s typical of Dennett to tell us smugly that the four atheist thinkers call themselves the Brights, with the implication those poor saps who find solace in religion are dim. Even an atheist such as me can find Dennett’s unremitting glee in his presumed intellectual superiority ugly. Unattractive too is Dennett’s incessant offloading of his accomplishments. Scuba diver, sailor, pianist, sculptor, cider maker and farmer. There is no end to (him going on and on about) his talents. He manages to make a scene in which he jammed as a student with saxophonist Gerry Mulligan in a Parisian jazz club devoid of charm. Which is a considerable feat.

His literary output since Consciousness Explained has involved arguing that many human phenomena are best understood in evolutionary terms. Everything evolves, be it religion, freedom, consciousness and, though don’t hold your breath, philosophy. In this he makes great use of his friend Richard Dawkins’s notion of memes, which are understood as the cultural equivalent to genes in that they are transmitted, randomly mutate and undergo natural selection.

In his best book, Darwin’s Dangerous Idea (1995), Dennett wrote, wonderfully, of what a philosopher unafraid to also be a student of science might achieve: “If you can approach the world’s complexities, both its glories and its horrors, with an attitude of humble curiosity, acknowledging that however deeply you have seen, you have only scratched the surface, you will find worlds within worlds, beauties you could not heretofore imagine, and your own mundane preoccupations will shrink to proper size, not all that important in the greater scheme of things.”

A noble aspiration, but in this book at least, Dennett’s inability to be humble gets in the way of its realisation.

• I’ve Been Thinking by Daniel C Dennett is published by Allen Lane (£30). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply