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John Locke The Limits of Human Understanding

Locke is often classified as the first of the great English empiricists (ignoring the claims of Bacon and Hobbes). This reputation rests on Locke's greatest work, the monumental An Essay Concerning Human Understanding. Locke explains his project in several places. Perhaps the most important of his goals is to determine the limits of human understanding. Locke writes:

For I thought that the first Step towards satisfying the several Enquiries, the Mind of Man was apt to run into, was, to take a Survey of our own Understandings, examine our own Powers, and see to what Things they were adapted. Till that was done, I suspected that we began at the wrong end, and in vain sought for Satisfaction in a quiet and secure Possession of Truths, that most concerned us whilst we let loose our Thoughts into the vast Ocean of Being, as if all the boundless Extent, were the natural and undoubted Possessions of our Understandings, wherein there was nothing that escaped its Decisions, or that escaped its Comprehension. Thus Men, extending their Enquiries beyond their Capacities, and letting their Thoughts wander into those depths where they can find no sure Footing; ‘tis no Wonder, that they raise Questions and multiply Disputes, which never coming to any clear Resolution, are proper to only continue and increase their Doubts, and to confirm them at last in a perfect Skepticism. Whereas were the Capacities of our Understanding well considered, the Extent of our Knowledge once discovered, and the Horizon found, which sets the boundary between the enlightened and the dark Parts of Things; between what is and what is not comprehensible by us, Men would perhaps with less scruple acquiesce in the avowed Ignorance of the one; and employ their Thoughts and Discourse, with more Advantage and Satisfaction in the other. (I.1.7., p. 47)

Some philosophers before Locke had suggested that it would be good to find the limits of the Understanding, but what Locke does is to carry out this project in detail. In the four books of the Essay Locke considers the sources and nature of human knowledge. Book I argues that we have no innate knowledge. (In this he resembles Berkeley and Hume, and differs from Descartes and Leibniz.) So, at birth, the human mind is a sort of blank slate on which experience writes. In Book II Locke claims that ideas are the materials of knowledge and all ideas come from experience. The term ‘idea,’ Locke tells us "...stands for whatsoever is the Object of the Understanding, when a man thinks." (Essay I, 1, 8, p. 47) Experience is of two kinds, sensation and reflection. One of these -- sensation -- tells us about things and processes in the external world. The other -- reflection -- tells us about the operations of our own minds. Reflection is a sort of internal sense that makes us conscious of the mental processes we are engaged in. Some ideas we get only from sensation, some only from reflection and some from both.

Locke has an atomic or perhaps more accurately a corpuscular theory of ideas.^[3] There is, that is to say, an analogy between the way atoms or corpuscles combine into complexes to form physical objects and the way ideas combine. Ideas are either simple or complex. We cannot create simple ideas, we can only get them from experience. In this respect the mind is passive. Once the mind has a store of simple ideas, it can combine them into complex ideas of a variety of kinds. In this respect the mind is active. Thus, Locke subscribes to a version of the empiricist axiom that there is nothing in the intellect that was not previously in the senses -- where the senses are broadened to include reflection. Book III deals with the nature of language, its connections with ideas and its role in knowledge. Book IV, the culmination of the previous reflections, explains the nature and limits of knowledge, probability, and the relation of reason and faith.