Locke, John (1632–1704)
Authors: Ayers Michael 
Published: September 2018

John Locke was the first of the empiricist opponents of Descartes to achieve comparable authority among his European contemporaries. Together with Newton’s physics, the philosophy of An Essay concerning Human Understanding gradually eclipsed Cartesianism, decisively redirecting European thought. Neoplatonic innatism was replaced with a modest, naturalistic conception of our cognitive capacities, making careful observation and systematic description the primary task of natural inquiry. Locke saw himself as carrying out just such a descriptive project with respect to the mind itself. Theorizing is the construction of hypotheses on the basis of analogies, not penetration to the essences of things by super-sensory means. In religion Locke took a similarly anti-dogmatic line, advocating toleration and minimal doctrinal requirements, notably in Epistola de tolerantia (A Letter concerning Toleration) and The Reasonableness of Christianity. Through his association with the Earl of Shaftesbury he became involved in government, and then in revolutionary politics against Charles II and James II. The latter involvement led to exile, and to Two Treatises of Government, a rejection of patriarchalism and an argument from first principles for constitutional government in the interests of the governed, and for the right of the misgoverned to rebel. Locke published his main works only after the ‘Glorious Revolution’ of 1688. He undertook important governmental duties for a time, and continued to write on many topics, including economics and biblical criticism, until his death. The Essay, Epistola and Second Treatise remain centrally canonical texts.
Locke held that all our ideas are either given in experience, or are complex ideas formed from simple ideas so given, but not that all our knowledge is based on experience. He accepted that geometry, for example, is an a priori science, but denied that the ideas which are the objects of geometrical reasoning are innate. ‘Experience’ includes ‘reflection’, that is reflexive awareness of our own mental operations, which Cartesians treated as a way of accessing innate ideas, but which Locke calls ‘internal sense’. To have ideas before the mind is to be perceiving given or constructed sensory or quasi-sensory images – things as perceived by sense. In abstraction, however, we consider only aspects of what is presented: for example, a geometrical proof may consider only aspects of a drawn figure, allowing generalization to all figures similar in just those respects. Universal knowledge is thus perception of a relation between abstract ideas, but we also have immediate knowledge, in sensation, that particular external things are causing ideas in us. This awareness allows us to use the idea as a sign of its external cause: for example, the sensation of white signifies whatever feature of objects causes that sensation. Representation is thus fundamentally causal: causality bridges the gap between reality and ideas. Consequently we have sensitive knowledge of things only through their powers, knowledge of their existence without knowledge of their essence. Each way in which things act on the senses gives rise to a phenomenally simple idea signifying a quality, or power to affect us, in the object. Some simple ideas, those of the ‘primary qualities’, solidity, extension, figure, motion or rest, and number (the list can vary) can be supposed to resemble their causes. Others, ideas of ‘secondary qualities’, colour, smell, taste and so forth, do not. We also form ideas of the powers of objects to interact.
Our idea of any sort of substantial thing is therefore complex, including ideas of all the qualities and powers by which we know and define that ‘substance’. Additionally, the idea includes the ‘general idea of substance’, or possessor of the qualities, a placemarker signifying the unknown underlying cause of their union. Locke distinguishes between the general substance, matter, and the ‘particular constitution’ of matter from which flow the observable properties by which we define each sort of substance – gold, horse, iron and so on. This ‘real constitution’ or ‘real essence’ is distinguishable only relatively to our definition or ‘nominal essence’ of the species. Locke extends this conceptualist view of classification to individuation in a famous, still influential argument that a person is individuated, not by an immaterial soul, but by unifying and continuous consciousness.
Because their real essences are unknown to us, we are capable only of probable belief about substances, not of ‘science’. In mathematics, however, real essences are known, since they are abstract ideas constructible without reference to reality. So too with ideas of ‘mixed modes’ and ‘relations’, including the ideas of social actions, roles and relationships which supply the subject-matter of a priori sciences concerned with law, natural, social and positive. The three legislators are God, public opinion and government. God’s authority derives from his status as creator, and natural or moral law is his benevolent will for us. Locke’s political theory concerns the authority of governments, which he takes to be, at bottom, the right of all individuals to uphold natural law transferred to a central agency for the sake of its power and impartiality. Economic change, he argues, renders this transfer imperative. In a state of nature, individuals own whatever they have worked for, if they can use it and enough is left for others. But with land-enclosure (which benefits everyone by increasing productivity) and the institution of money (which makes it both possible and morally justifiable to enjoy the product of enclosure) this primitive property-right is transcended, and there is need for an authority to ordain and uphold rules of justice for the benefit of all. Any government, therefore, has a specific trust to fulfil, and should be organized so as best to safeguard this role. A ruler who rules in his own interest forfeits all rights, as a criminal at war with his subjects. Then rebellion is justified self-defence.