An Essay Concerning Human Understanding | Study Guide

John Locke

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An Essay Concerning Human Understanding | Vol. 2, Book 2, Chapters 22–24 : Of Ideas | Summary



Vol. 2, Book 2, Chapter 22: Of Mixed Modes

Mixed modes, Locke says, are complex ideas formed from simple ideas of different kinds. Examples include "drunkenness" and "obligation." People put these ideas together voluntarily and sometimes with effort, often learning the words for them before they get a clear sense of the idea itself. For instance, someone may learn the word "drunkenness" without either becoming inebriated or seeing anyone in that state. Mixed modes are often culture-specific—Locke gives the example of "ostracism," the ancient Greek practice of exiling unwanted citizens by a popular vote. This idea, he observes, was unique to the Greeks, and there was no word for it in the languages of neighboring civilizations. Locke concludes the chapter by showing that mixed modes, like their simpler cousins, can arise in the mind purely through sensation and reflection.

Vol. 2, Book 2, Chapter 23: Of Our Complex Ideas of Substances

Locke has already (in Book 2, Chapter 13) complained about other philosophers' overemphasis on the idea of substance, the underlying essence that makes gold gold or makes a horse a horse. If we understood the underlying physical properties (the primary properties) of different objects, Locke concedes, the concept of substance as such might be more useful. For practical purposes, however, Locke deems it better to think of substances as collections of simple traits which always coincide. Thus, gold is defined by its shiny yellow color, its malleability, its density, and so forth. All of these, Locke says, might eventually be traced to the properties of the "minute particles" which make up gold. Nonetheless, Locke holds out little hope that we will ever fully understand the physical universe. Our senses and intellectual faculties, he maintains, can only go so far.

Next, Locke launches into a long digression on the subject of spirits, which he regards as substances of another sort. He defends his opinion that spirits, despite lacking bodies, are capable of physical motion. Even in spiritual matters, Locke maintains, we get all our knowledge from sensation and reflection, and we know nothing for certain but what we can capture in simple ideas. Everything else is abstraction or conjecture.

Vol. 2, Book 2, Chapter 24: Of Collective Ideas of Substances

This chapter extends the previous discussion to deal with collective ideas, such as "army" or "fleet." Though formed by sticking together constituent ideas, Locke says, these collective ideas become as distinct and singular in the mind as non-collective ideas like "man" or "ship." Collective ideas are "the artificial draughts of the mind," bringing things which are "remote" and "independent" into a single frame of view.


In Chapter 23 Locke anticipates another objection from his critics. "How do we know about spirits," he imagines them saying, "if we have no direct experience of them? "Locke's rebuttal is that we don't, generally speaking, "know" about spirits at all. We have beliefs and ideas about them, but these beliefs and ideas are hard (often impossible) to test from within the confines of this earthly life. For Locke, there are extremely few non-negotiable propositions about the spiritual world—ideas of which we can be so certain as to call them "knowledge." These include the existence of the soul and the existence of God, the latter of which Locke explores in Book 4, Chapter 10. Notably, these are two of the ideas which Descartes upheld as necessarily innate in his Meditations (see Context). Locke, however, argues that both can be discovered and affirmed through experience alone.

More broadly, Locke uses these chapters to lay some of the groundwork for his discussion of knowledge in Book 4. In Chapter 23 he declares that "we know nothing beyond our simple ideas," thus setting a definite and severe-sounding boundary to human understanding. But the statement is not quite as harsh as it might seem. In Book 4 Locke will develop a very narrow definition of knowledge, one based on a standard of perfect certainty and provability. By these criteria, we really do know "nothing" except what we can directly, immediately experience. From the viewpoint of modern psychology, even this stringent definition is somewhat generous, since our senses can mislead us in myriad ways. Many of the ideas Locke calls "simple" are precisely the ones that are sabotaged by effective optical illusions. People encountering the famous checker-shadow illusion "know" one square is white and the other black, when in fact both squares are gray.

Yet the lack of absolute knowledge is not as much of an impediment as it might seem at first. As Locke freely admits, we don't get on in the world by rigorously testing every proposition we come across. If we waited for perfect certainty, we'd never make any decisions at all, because true certainty about most things is impossible. Rather than letting this fact paralyze us, we use our best judgment to determine what is likely and what is unlikely. We act, ultimately, on the basis of probability, not knowledge.

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