 We have the Ideas of Matter and Thinking, but possibly shall never be able to know, whether any mere material Being thinks, or no; it being impossible for us, by the contemplation of our own Ideas, without revelation, to discover whether Omnipotency has not given to some System of Matter fitly disposed, a power to perceive and think, or else joined and fixed to Matter so disposed, a thinking immaterial Substance…. (Locke 1690 IV, iii, 6 [1975: 540–1]) 