The English philosopher John Locke (1632–1704) was born in Bristol and raised as a Puritan. He was educated at Christ Church, Oxford University, where he became a tutor in Greek rhetoric and philosophy. Later he was a practicing physician and assistant to Lord Ashley, the Earl of Shaftesbury. In 1683, because of the Earl of Shaftesbury's anti-Stuart political views, Locke was forced to flee to the Netherlands. There he wrote his two great masterpieces: An Essay Concerning Human Understanding (published in 1689), from which our selection is taken, and Two Treatises on Civil Government (published in 1690). He returned to England in 1689, wrote his final work, The Reasonableness of Christianity, and died in 1704.
Locke's work in the theory of knowledge is the first systematic assault on Cartesian rationalism, the view that reason alone guarantees knowledge. Locke argued that if our claims to knowledge make any sense, they must be derived from the world. He rejects the rationalist notion that we have innate ideas (actual knowledge of metaphysical truths, such as mathematical truths, universals, and the laws of nature) because (1) there is not good deductive argument establishing the existence of such entities; (2) children and idiots do not seem to possess them; and (3) an empirical way of knowing, which seems far more reasonable, has no place for such entities.
According to Locke, the mind at birth is a tabula rasa, a blank slate. It is like white paper, devoid of characteristics until it receives sense perceptions. All knowledge begins with sensory experience upon which the powers of the mind operate, developing complex ideas, abstractions, and the like. In place of the absolute certainty that the rationalists sought to find, Locke says that apart from the knowledge of the self, most of what we know we know in degrees of certainty derived from inductive generalizations. For example, we see the sun rise every morning and infer that it is highly probable that it will rise tomorrow, but we cannot be absolutely certain.
Locke holds a Representational Theory of Perception in which objects in the world cause our sense organs to start processes that result in perceptual experience. We are never aware of the thing in itself, the object which is perceived and which causes the idea to arise in our mind, but only the idea or representation of the object. We are directly aware of the idea but in as much as the object is the cause of the idea, we may be said to be indirectly aware of the object itself.
Locke held a causal theory of perception in which processes in the external world impinge on the perceiver's sense organs, which in turn send messages to the brain, where they are transformed into mental events. We may diagram the Causal Theory of Perception this way: