Locke was born in 1632 in Somerset, England, to a Protestant landowner. At the age of fifteen, he enrolled in the Westminster School before going on to Christ Church, Oxford. In 1666 he met Anthony Ashley Cooper (the future Earl of Shaftesbury), who was to become his patron and whom Locke was to serve as secretary for much of his life. Locke shared the political vicissitudes of Shaftesbury's career and fled to the Netherlands in 1683, fearful of being charged with treason. After the Glorious Revolution, Locke returned to England; from 1692 until his death, he resided with Sir Francis and Lady Masham, the daughter of Ralph Cudworth.

Locke's main metaphysical and epistemological work is the mammoth An Essay concerning Human Understanding, which he published in 1689 and revised five times before his death. Although Locke rarely mentions Descartes by name in the Essay, much of that work can profitably be read as a running battle with him. Many of Descartes’ key positions – on innate ideas, the essence and immateriality of the soul, the nature of body as extension – come under attack.

Locke rejects Descartes’ doctrine of innate ideas. If the doctrine means that we have ideas before we are aware of them, it is self-contradictory, for no idea can be in the mind without our being aware of it. If, as Descartes sometimes suggests, it means only that we have a capacity or disposition to form certain ideas, then it is trivially true of all ideas (I.ii.5). Nor does Locke have any use for the Cartesian intellect. In the Sixth Meditation, Descartes uses the example of a chiliagon to show that we have a capacity for forming ideas that outstrips our ability to generate images. The idea of the chiliagon must then come from the intellect. Against this, Locke argues that, while we have no idea of the figure of the chiliagon, we can reason about its properties by attending to the idea of the number of its sides (II.xxix.13).