There has, of course, been progress. Neuro­science can nowadays can give a fascinating, if still incomplete, account of what makes the difference in the brain between wakefulness and sleep; of how we sense the world; of how we learn, remember and communicate; of our emotions and our drives; of how we allocate attention, plan our actions, implement them. Even the most elusive yet most precious elements of our experience are becoming accessible to science. As you gaze at the face of your true love, areas linked to critical social appraisal fall quiet; calling an image to the mind’s eye, the brain produces a soft echo of what happens when we see; illusions of movement result from perfectly real activation of regions of the brain that signal motion; a shiver down the spine from a favourite moment of music expresses strong activation in the circuitry of emotional — and sexual — reward; the eerie experience of déjà vu arises from inappropriate activity in areas of the brain that tag familiarity.

Discoveries like these suggest that, as we learn more about the brain, we should become able to show that experience tracks its activ­ity, hugging it curve for curve. Yet many of us remain unsatisfied — like Leibniz who, early in the 18th century, imagined walking into an artificial mind and finding nothing that could explain experience: “supposing there were a machine so constructed as to think, feel and have perception, we could conceive of it as enlarged and yet preserving the same proportions, so that we might enter into it as into a mill. And this granted, we should only find on visiting it, pieces which push against one another, but never anything by which to explain perception.” This is the “hard question” of consciousness, the “explanatory gap”: how can what happens in a brain ever give rise to what passes through a mind? It is the problem that the tough-minded physiologist Charles Sherrington described as an “embarrassment” for biology. To his frustration he could not see the way to a solution, and lamented: “to man’s understanding the world remains obstinately double”, a double act of matter — life and mind.