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Berkeley published An Essay Towards a New Theory of Vision in 1709, at the age of 24. In it he inveighed against the dominant analysis of vision in terms of optics and in its stead placed touch at the centre of visual perception. He is shown, on the left, in the title page of the book. Berkeley based his new theory on certain phenomena that were taken as self-evident, like the perception of distance and upright vision. His Essay is perhaps best seen as laying the ground for his esse: his famous phrase “esse est percipi” – to be is to be perceived – which was published in his Treatise Concerning the Principles of Human Knowledge published in 1710. That is, the matter from which materialism is constructed is itself open to question. If all we have are our perceptions, how can we prove the existence of an external world? A problem with this position is that if perceptions are transitory so is existence. Does an object cease to exist when the eyes are closed? Berkeley sought to salvage this slide into solipsism (that nothing other than one’s own ideas exists) by arguing that God alone perceived an external reality. Hence his theoretical approach is referred to as idealism. On the right, Berkeley’s words ESSE EST PERCIPI are presented repeatedly, and in them his portrait exists if it can be perceived. Following extensive travels throughout Europe he journeyed to America in 1728 with the plan of setting up a missionary college in Bermuda. His long voyage finally terminated at Newport, Rhode Island, and he remained there until 1731, returning to London without setting foot in Bermuda. He was appointed Bishop of Cloyne in 1734, a post he occupied for most of the rest of his life. The Scottish painter John Smibert (1688-1751) accompanied Berkeley to America, but he settled in Boston and became a prominent colonial portraitist. Smibert painted the portrait of Berkeley a detail of which is used in the illustration on the left.