An Essay Concerning Human Understanding | Study Guide

John Locke

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An Essay Concerning Human Understanding | Vol. 2, Book 4, Chapters 7–9 : Of Knowledge and Probability | Summary



Vol. 2, Book 4, Chapter 7: Of Maxims

Locke next turns his attention to maxims, a group of self-evident statements which are taken as fundamental and often regarded as innate. Being self-evident, he says, is not a good criterion for innateness because so many statements possess it. The statement "red is not blue" is just as self-evident as "the whole is greater than any of its parts." Moreover, Locke asserts, maxims (also called axioms) "do not much influence our other knowledge," partly because they are not the first truths we encounter. We do not, he insists, derive our specific knowledge from general rules. Rather, we derive these so-called maxims from many specific instances. Ultimately, Locke finds maxims to be of limited use outside of formal academic debates. He suggests they may even prove dangerous if, underneath the impressive-sounding language we use, we lack clear and distinct ideas.

Vol. 2, Book 4, Chapter 8: Of Trifling Propositions

Almost as bad, says Locke, are "trifling propositions"—statements which are trivially true and thus "bring no increase to our knowledge." Statements of identity, such as "A is A" or "a horse is a horse," are the most numerous group. Mere definitions are also "trifling" in that they "teach ... the signification of words" without adding any real knowledge. Many other impressive-sounding propositions also count as "trifling" in Locke's book because they are really just rearrangements of terms. Practitioners of philosophy and "school-divinity," he says, often make grand statements about "God," "humanity," and "the soul" without defining those words. This, to Locke, is much like computing sums of money without any idea what a "pound," a "shilling," or a "penny" is. Finally, Locke notes that changing a word's meaning without warning is a form of "trifling." He concludes with some guidelines for spotting these useless propositions in writing and speech.

Vol. 2, Book 4, Chapter 9: Of Our Knowledge of Existence

"Our knowledge of our own existence is intuitive," Locke affirms—meaning we know it immediately and directly, without the need for proof or demonstration. In contrast, our knowledge of God is demonstrative (i.e., requiring proof). Our knowledge of the existence of everything else—including the whole physical world—comes through sensation, meaning it has all the limitations of our senses. The latter two categories, the existence of God and the existence of other things, are explained more fully in subsequent chapters.


This group of chapters centers on the theme of useless or suspect knowledge. Maxims, Locke says, are often employed for show and seldom help us to gain worthwhile knowledge of a subject. "Trifling propositions" are, likewise, frequently used to impress listeners and silence opponents, but they rarely (in Locke's view) have a genuine educational purpose. Locke will later (in Chapter 17) advance many of the same criticism about syllogisms, a set of logical rules used to test the validity of arguments. Like maxims, syllogisms will be painted as a needlessly formal apparatus for doing something the mind does naturally.

The misuse of philosophical language is a pet peeve of Locke's, probably a holdover from his frustrating student years at Oxford (see About the Author). Accordingly, Locke unloads with some of his most colorfully sarcastic imagery when he critiques such abuses. The result is a set of chapters which are vivid and even funny at times, despite the dry subject matter. Locke takes down the "school-divinity" set by, essentially, comparing them to a child who pretends to be rich in Monopoly money. He has even harsher words for those who inflate their speech with "A is A"-type propositions: "It is but like a monkey shifting his oyster from one hand to the other; and had he but words, might, no doubt, have said, 'oyster in right hand is subject, and oyster in left hand is predicate:' and so might have made a self-evident proposition of oysters, i.e., oyster is oyster." In other words, people who rely on such a rhetorical strategy are "aping" knowledge without doing anything truly clever or productive.

Locke seems quite sure that axioms or maxims, as rules of reasoning, are not innate. Modern psychological research throws this assertion in a fresh and interesting light. Although it may be true that people come into the world without formal logical rules, they do have some strong and seemingly innate tendencies in the ways they process information. In their landmark Science paper "Judgment under Uncertainty: Heuristics and Biases" (1974) Amos Tversky and Daniel Kahneman argued that humans rely on a remarkably consistent set of informal reasoning strategies, called heuristics. These heuristics lead people to err predictably (cognitive bias) when faced with certain types of situations. Tversky and Kahneman's research sparked a much wider exploration of these issues among psychologists, an effort known as the heuristics and biases program. Kahneman, who went on to win the Nobel Prize in Economic Sciences in 2002, summarized many of the resultant insights in his 2011 book Thinking, Fast and Slow.

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