‘It would be very singular,’ wrote Voltaire, ‘that all nature, all the planets, should obey eternal laws, and that there should be a little animal, five feet high, who, in contempt of these laws, could act as he pleased, solely according to his caprice.’ It is an eloquent statement of the problem of free will, and it is the place where our figments run slap up against reality, like the proverbial irresistible force meeting the immovable object. We have a distinct, overwhelming impression that we have a free choice concerning the actions that we take: free, that is, subject to the evident constraints of physical law. We cannot choose to float into the air, for example. Yet there is absolutely nothing in the inorganic world that possesses that kind of freedom.