On behalf of us all, Eric Harrison poses the ultimate question: when we die does our soul live on?

When Shakespeare said, "To thine own self be true", he was quoting a proverb that had its roots in ancient Greece. "Examine yourself," said Socrates, who argued that self understanding is essential for happiness and the pursuit of any knowledge whatsoever. It is little exaggeration to say that all of Western psychology and science starts with Socrates' little phrase.

When I look at myself, however, I see an endless cavalcade of sensations, emotions, memories and habits within in one everchanging body. I seem to be too big, too complicated, too disconcertingly variable to nail down in any meaningful way. And yet, despite all this, I still know exactly who I am. I will never mistake myself, nor be mistaken, for any other human being.

This gut feeling of individuality comes from a place that precedes words. Even amoebas, with the most minimal degree of consciousness, and no understanding of language, can recognise self and not self. If nothing else, this ability is essential for the functioning of the immune system and thus life itself. Thanks to the vagaries of sexual reproduction, every living thing is utterly unique, and vigorously protects its autonomy.

But does a bug have a soul? Aristotle thought so. He quite sensibly regarded the soul as the integrating intelligence of any living organism, including animals and plants. But this hasn't stopped people in the past from trying to draw lines in the sand.

It goes without saying that educated males have always had souls. But at different times in history, women, slaves, Negroes, Asiatics, those of different religions and even the lower classes have been regarded as soulless, and therefore ripe for exploitation. And that is just referring to human beings. Now that we know we share 98 per cent of our genome with apes, and 60 per cent with fruit flies, it becomes so much harder to regard ourselves as quintessentially superior.

But is the soul immortal? Aristotle defined the "soul" as being virtually the same as "life". Consequently, when the body dies the soul does, too. According to him, the soul, or "anima", is that which animates all living things, including plants and animals. "Psyche", another old word for the soul, literally means "breath" and "life" in the same sense as the Sanskrit word "prana" and the Chinese word "chi". The soul is fundamentally that which keep us alive and well. Shaw calls it "the life force"; Bergson calls it "the vital spirit"; Schopenhauer calls it "the will to live".

Aristotle also said that the soul has different levels of functioning. The first is life itself, which even plants possess. The second involves functions such as the kinds of memory, emotion and judgement that animals have. The third is "human" reason, our usual mode of operating. The fourth level is the capacity for self reflective, abstract, independent thought, or "Reason" with a capital R. This is what Descartes, who was also a great mathematician, regarded as the most glorious function of the soul.

The soul in all its complexity is unimaginably smart, far smarter than our conscious minds. Our biological, self regulatory mechanisms keep us from excess. Our emotions keep us safe and satisfied. Even our intellectual activity is clearly shaped and guided by deeper forces. Aristotle describes all these as functions of the soul.

All this, however, is dependent on being alive. When the being dies, the soul does, too. The soul, after all, equals "life". It is anchored in biology and, as such, can't be immortal. So where does the myth of the immortal soul come from?

Meister Eckhardt, the 14th century German mystic, said the soul also contained a "scintilla", or spark of the divine. We recognise this most vividly when mind looks back on itself and becomes entranced by its own radiance, its capacity to see. In this state, the soul seems to transcend the usual objects of consciousness, and thus time and space itself. It sees what seems to be the Absolute.

When mystics try to describe this experience, they typically say it is eternal, infinite and beyond matter. They also say it is our true nature. The Indian formula is that "atman is Brahman". The individual soul becomes one with God, and is therefore equally immortal.

The mystical vision is often described as the insight that all is one transcendental consciousness, and that nothing of real importance ever dies. Only people. And leopards. And polar bears. And dragonflies. Unimportant things. I do have my doubts about the mystical vision.

So is this the Truth, or is it just a vision? Can a deep conviction of eternal life be regarded as any kind of proof at all? Or is "eternity" just a metaphor for an experience which, by its very nature, is transient? Is the soul the deep, organic intelligence of the whole body and mind, which is bound to disintegrate like all living things, just as Aristotle says? Or is it some pure essence – a ghost in the machine – that lives forever, even when the body dies?
As human beings, we are very good at holding contradictory opinions simultaneously. There must be some evolutionary advantage in it. I am always astounded that it is so easy for people to believe in life after death, although the evidence to the contrary could not be more overwhelming. Everything that lives dies, and always has. Not a single one of the countless billions of living beings since time began has escaped death. Yet we find it so easy to believe that we can't "really" die. It is virtually our default position.

It is easy to imagine dying. It is like being sick, only worse. But it is impossible to imagine being dead. We have to be alive to do so. Parmenides, 2600 years ago, drew the logical conclusion from this that death is a fiction, and that, in fact, nothing ever dies. Ramana Maharshi, the Indian sage, about a hundred years ago, came to exactly the same conclusion. He could imagine his body dying and being cremated, but he couldn't imagine the death of his consciousness. He therefore concluded that his consciousness had to be immortal.

Ramana spent the rest of his life in almost total silence, isolation and inactivity, refining this conviction. He spent decades doing virtually nothing at all except sitting and sleeping. He even let people feed and bathe him, like a baby. Although he eventually started to teach, he was probably one of the most peaceful men who have ever lived. His photos show a face of vacuous serenity. Yet when he died of cancer at the age of 73, I'm sure his "immortal" consciousness died with him, despite what he believed.

I suspect that the conviction that we can't "really" die has something to do with our clumsy, cobbled together, perception of time. To me, the future beyond the next week or two seems more like an idea than a fact. I thoroughly sympathise with people who spend every penny they earn because the future seems so bloodless.

We are not hardwired to understand the passage of time. We have to learn it. It seems that we are only conscious of time because we notice movement. Our bodies move, our minds move, the world moves around us. Over the years, we develop a working sense of passing time by reading this constant sensory input, but it is always approximate, and something of an effort, and frequently breaks down.

This sense of time can easily vanish if the movement around and within us slows down or stops. In deep meditation, when the mind falls silent, and the body becomes very still, the sense of passing time can collapse. In this state, the breathing virtually stops, and the space between out-breath and in-breath can seem to last forever.

To look inwards, to have no thoughts, no sense of the body or personal identity, and no awareness of any movement paradoxically results in total bliss. It is an experience of infinity and eternity even though, from another perspective, it may only last a few seconds of clock time. A good yogi, like Ramana Maharshi, can enormously enhance that sense of timelessness until it feels like second nature to him. To perfect this state, however, demands a profoundly narcissistic withdrawal from the world, which few intelligent people would feel was worth the sacrifice.

The other way we feel eternity is to recollect the mindstate of childhood, before we really developed our sense of time. Unlike Ramana Maharshi's cold detachment, this is a state of connectedness and love. The metaphysical poet Thomas Traherne, 250 years ago, exquisitely described this feeling of being a little child enchanted by the world:

"All appeared New and Strange at the first, inexpressibly rare, and delightful and beautiful. I was a little stranger which at my entrance into the world was saluted and surrounded by innumerable joys.

"The Corn was Orient and Immortal Wheat, which should never be reaped nor was ever sown. I thought it stood from Everlasting to Everlasting. The Dust and Stones of the Street were as precious as Gold. The men! Immortal cherubims! I knew not that they were Born or should Die. But all things abided Eternally as they were in their Proper Places. Eternity was manifest in the light of the Day, and something Infinite behind everything appeared."

I am quite certain that we are not "spiritual beings", capable of surviving the death of the body. I find the concept of an immortal soul very silly indeed if taken literally, but it does have one great virtue. It tells us that we really can know infinity and eternity as an experience, if not as an empirical fact. Through stillness and silence, it is quite possible to escape the dreary plod of time. On our noisy and polluted Earth, every inch of which is stalked by death, we can still see the face of God.