What is consciousness?

The hard problem. Defining what is means to be human.

“I THINK, therefore I am.” René Descartes’ aphorism has become a cliché. But it cuts to the core of perhaps the greatest question posed to science: what is consciousness? The other phenomena described in this series of briefs—time and space, matter and energy, even life itself—look tractable. They can be measured and objectified, and thus theorised about. Consciousness, by contrast, is subjective. As Descartes’ observation suggests, a conscious being knows he is conscious. But he cannot know that any other being is. Other apparently conscious individuals might be zombies programmed to behave as if they were conscious, without actually being so.

In reality, it is unlikely that even those who advance this proposition truly believe it, as far as their fellow humans are concerned. Cross the species barrier, however, and matters become muddier. Are chimpanzees conscious? Dogs? Codfish? Bees? It is hard to know how to ask them the question in a meaningful way.

Moreover, consciousness is not merely a property of having a complex, active brain, for it can vanish temporarily, even while the brain is healthy and functional. Most people spend a third of their lives in the state described as “sleep”. Unless awoken while dreaming, they have no sense of being conscious during these periods. Recordings of the brain’s electrical activity show, though, that a sleeping brain is often as busy as one that is awake. Subjective though it is, consciousness therefore looks like a specific phenomenon, not a mere side-effect. That suggests it has evolved, and has a biological purpose. These things—specificity and purpose—give researchers something to hang on to.