An Essay Concerning Human Understanding | Study Guide

John Locke

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An Essay Concerning Human Understanding | Vol. 1, Book 2, Chapters 25–28 : Of Ideas | Summary



Vol. 1, Book 2, Chapter 25: Of Relation

Relations are the third and final kind of complex idea, serving to yoke things together. As with modes and substances, not all relations have names, and some (e.g., "concubine") have names in some languages but not others. Locke points out that "some seemingly absolute terms," like "old," are actually relative; he promises to expand on this idea later (and does so in Chapter 26). Relations, like other complex ideas, are built up of simple ideas and can be traced back to those simple ideas—a project Locke undertakes in the following chapters.

Vol. 1, Book 2, Chapter 26: Of Cause and Effect

Ideas of cause and effect, Locke says, arise through observation. We see that wood always becomes ashes when exposed to fire, and we infer that the fire causes wood to change into ashes. Special types of causal relations include creation (making something out of nothing), generation (e.g., of offspring), making (e.g., of artwork), and alteration. Locke next considers "relations of time," returning to his contention that "seemingly absolute terms" can have a relative meaning. A man, for example, is called young at twenty, but a horse of the same age is old. The same goes for "relations of place and extension," as well as those of power. Thus, "a weak man" is weak relative to other men.

Vol. 1, Book 2, Chapter 27: Of Identity and Diversity

The most philosophically interesting relations for Locke, however, are those of "identity and diversity" (i.e., of sameness and difference). Locke considers first what makes a plant or an animal "the same" at different points in time, given that its physical makeup is constantly changing. He determines that for any living thing, including a man, identity consists in "a participation of the same continued life" in "the same organized body." Thus, even if two (living) bodies shared the same soul, each one would be a distinct "man." They would not, however, be different "persons," which for Locke is a different term with a different meaning. Personal identity, he says, consists in consciousness. Consequently, if a soul could travel back and forth among different bodies, it would still be a single person. Since "self depends on consciousness," if someone were to lose their memory entirely, they would in effect become a different person. This—personal identity, and not merely being the same "man"—is the proper basis for decisions having to do with right, wrong, praise, and blame. To Locke, it is unfair to hold someone accountable for acts they truly cannot remember committing.

Vol. 1, Book 2, Chapter 28: Of Other Relations

Among the remaining relations, the most significant are laws, of which Locke identifies three kinds: divine, civil, and philosophical. Divine law is handed down by God and is "the measure of sin and duty." It is often ignored, Locke points out, because its rewards and punishments are supposed to take effect only in the afterlife. Civil law, "the measure of crime and innocence," is what we typically think of as "law." It operates through courts and is seldom ignored in day-to-day life because its punishments and rewards are "ready at hand." Finally, Locke identifies philosophical law as "the measure of virtue and vice"—in essence, the court of public opinion. This "law" varies greatly from place to place but is usually respected, because people cannot bear to be shunned or hated by the others in their community. Morality, Locke maintains, is "the relation of actions to these rules,"—the tendency to pursue what is considered good or evil, legal or illegal, virtuous or vicious.


Locke's discussion of personal identity in Chapter 27 is one of the highlights of the Essay. It offers a way of thinking about consciousness that is based on continuity of mind, not of body. The concept of identity Locke proposes is resilient and flexible. It is able to address medical phenomena, such as amnesia, just as easily as it addresses spiritual beliefs like reincarnation.

Yet as Nigel Warburton points out in Philosophy: The Classics (2006), Locke's notion of identity becomes problematic when one considers the much less dramatic forgetting that occurs throughout life. Locke himself observes that our memories are "laid in fading colors" which are apt to "vanish and disappear." He doesn't, however, trace this thought's implications for his model of personal identity. It was left to an early critic of Locke's—fellow philosopher Thomas Reid (1710–96)—to make the connection.

In his Essays on the Intellectual Powers of Man (1785), Reid describes a man in three stages of life: boyhood, adulthood, and old age. The adult can remember his boyhood actions clearly and so, according to Locke's definitions, is the same person as the boy. The old man can remember his actions from early adulthood onward, making him "the same person" as the younger adult. The old man cannot, however, recollect his boyhood experiences. Thus, it seems the old man both is and is not the same person as his boyhood self. For Reid—and for Warburton, who reports Reid's thought experiment—this example casts doubt on the consistency of Locke's theory of identity.

Other challenges arise from modern psychological studies showing a person can lose much of their memory while still retaining the core facets of their personality. In his 2013 book The Power of Habit, Charles Duhigg tells the story of one such person, an elderly man known in the medical literature as "E.P." Having suffered from a bout of viral encephalitis, E.P. sustained severe but localized damage to a region of his brain responsible for short-term memory. As a result, he not only suffered from retrograde amnesia, but had extreme difficulty forming new memories—often forgetting, for instance, what he had for breakfast. Yet, according to his wife and the researchers who studied him, E.P. retained many aspects of his past personality. Cases like E.P.'s help to underscore what Locke himself acknowledges in his "under the influence" example: memory loss, gradual or acute, seldom represents a complete break with one's past personality. Although this fact does not invalidate Locke's definition, it shows how problematic memory can be as a criterion for personal identity.

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