Locke, John (1632–1704)
Authors: Anstey Peter 
Published: September 2018

John Locke was the leading English philosopher of the late seventeenth century. His two major works, An Essay concerning Human Understanding and Two Treatises of Government, both published in 1690, have exerted enormous influence on subsequent thought, particularly in metaphysics, theory of knowledge and political philosophy. Locke’s writings were central to the philosophy of the Enlightenment in the eighteenth century and set the terms of reference for modern liberalism.

Educated in the arts at Oxford, a friend of Robert Boyle and Isaac Newton, and a close associate of the leading politician the first Earl of Shaftesbury, Locke’s intellectual range was broad. He trained as a physician, dabbled in chemistry and botany and throughout his life kept abreast of developments in natural philosophy. At the same time, he developed theories of natural law and religious toleration, contributed to debates on contemporary economic issues, wrote a primer on the philosophy of education, defended the reasonableness of Christianity and maintained an extensive correspondence and intellectual network. It was not until the publication of the Essay when Locke was in his late 50s, however, that he became a public intellectual.

The Essay provides an analysis of the scope and limits of the faculty of human understanding, using a sophisticated theory of ideas. It contains four books, the first of which seeks to refute the view that the mind contains innate metaphysical and moral principles. The second book sets out Locke’s theory of ideas and contains original and penetrating treatments of the nature of the will and motivation and the nature of personal identity. It also contains Locke’s theory of material qualities with his famous distinction between primary and secondary qualities, and discussions of the nature of substance, duration, infinity and the association of ideas. Book Three deals with the nature of language, the theory of essences, and provides an account of the way in which humans divide substances into species. Book Four uses the resources set out in the preceding books to develop a theory of knowledge and belief and to explore the differences between faith and reason.

Central to Locke’s project is the view that all knowledge is constructed out of ideas. Knowledge in its most basic form is nothing but the perception of the agreement or disagreement of ideas and ideas can only be acquired through the senses or through introspection on the operations of our minds. Once the understanding is furnished with enough simple ideas from these two sources of experience, it sets about constructing complex ideas, forming propositions out of its various ideas and giving the ideas names. Locke is fundamentally opposed to the view that knowledge and reason begin with a set of basic principles or maxims, such as that the whole is the sum of its parts. This is the motivation for his arguments against the claim that principles are innate. Instead we must construct the principles of all the different sciences from scratch out of our stock of ideas.

In the cases of mathematics and morality this can be achieved. In the case of our knowledge of the sorts or species of substances we encounter in the external world, however, we are significantly constrained. This is because our senses are limited and we do not have epistemic access to the inner natures of things. We can see many effects but the underlying causes of those effects, such as magnetism or cohesion, are out of reach. As a result, Locke is pessimistic about the prospects of natural science, though he does believe that the method of experimental philosophy, particularly natural history, gives us the best chance to extend our knowledge of the natural world. Moreover, he believes that of all the speculative systems of natural philosophy, the corpuscular view of matter is the most intelligible.

Locke’s political philosophy gives us some insight into his conception of the form that a demonstrative moral philosophy might take. However, the precise relation between the Two Treatises and the Essay remains a controversial issue. The starting point for Locke’s view of the formation of civil society is the natural equality of every human being. We are equal in freedom and equal in both power and obligation with respect to the law of nature. However, in the absence of civil society – that is, in the state of nature – we suffer many inconveniences, particularly with regard to protecting property and applying the law of nature. It is only by consenting to give up our basic power to enforce the law of nature, a power that is common to all, to an authority, that we are able to overcome the inconveniences of the state of nature. In so doing, we secure the integrity of our property, that is, our life, liberty and possessions. The handing over of our basic power does not render us politically impotent however. For, should the government, whether a democracy, oligarchy or monarchy, break the people’s trust, the citizens have a right of resistance and can dissolve the government.

Locke’s Two Treatises was published anonymously and did not embroil him in ongoing debate in his own day, though its subsequent influence was profound. The same cannot be said of another anonymous work, his A Letter Concerning Toleration, which argued that religious toleration should be extended to all but atheists and those who submit to foreign authority. The most vigorous reaction to Locke’s writings, however, was to the Essay, particularly to Locke’s account of personal identity as continuity of consciousness and his suggestion that matter fitly disposed might have the power of thought. These two issues are indicative of the rich philosophical resources within the Essay, both in its positive theses and its illustrative material, which have ensured that this work continues to be read and studied with profit today.