An Essay Concerning Human Understanding | Study Guide

John Locke

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An Essay Concerning Human Understanding | Vol. 1, Book 2, Chapters 18–21 : Of Ideas | Summary



Vol. 1, Book 2, Chapter 18: Of Other Simple Modes

Locke now rounds out his discussion of simple modes, previously defined as modes "contained within the bounds of one simple idea" (Book 2, Chapter 12). He lists varieties of motion, sound, color, taste, and smell as further examples. Many of these modes have no names, but this does not stop people from having clear and distinct ideas of those modes. Locke observes that people generally give names to ideas only if they encounter those ideas frequently. Thus a chemist might have names for different laboratory techniques, while a blacksmith might have names for different ironworking tools.

Vol. 1, Book 2, Chapter 19: Of the Modes of Thinking

In this quick chapter Locke extends the concept of a simple mode to the activities of the mind. Modes of thinking, he says, include such processes as "study," "attention," "dreaming," and even religious ecstasy. His main point is that thinking is something the mind does, and not the mind's "essence" in some mystical way. The mind doesn't, for instance, stop existing when someone is in a dreamless sleep and then suddenly reappear when they wake up. Rather, the mind is there the whole time, though dormant.

Vol. 1, Book 2, Chapter 20: Of Modes of Pleasure and Pain

Locke then applies the "mode" treatment to the simple ideas of pleasure and pain. In his scheme, love, hatred, desire, and fear are all "modes of pleasure and pain" because all of them are mental attitudes related to those two basic phenomena. Even the most complicated emotions, Locke argues, have some relationship to pain and pleasure, and thus to the two main sources of ideas: sensation and reflection.

Vol. 1, Book 2, Chapter 21: Of Power

This marathon chapter does much more than its simple label would imply. In it Locke first distinguishes between two kinds of power: passive and active. Passive power is the ability of a body set into motion to "transfer" that motion to something else. A billiard ball, for example, has the passive power to move other balls on the table if it comes into contact with them. But the ball only has this "power" because it has been struck by the cue. Active power, in contrast, is the ability to "cause" motion, and not merely to transfer it. For Locke, this is an attribute of "spirits," including the human mind. Actively willing our bodies to move is, he says, an act fundamentally distinct from being passively moved about.

The meat of the chapter is in Locke's discussion of free will. For Locke, will is a "power to begin or forbear, continue or end several actions of our minds, and motions of our bodies." Liberty is the ability to actually implement one's will. Taking these definitions as his starting point, Locke says it is absurd to ask "whether will be free." The will is fundamentally not free in that we cannot help wanting things, and we cannot help preferring certain things over others. These preferences, in turn, are constrained by our inborn inclination to seek pleasure and shun pain. The differences in human activity are based on our different ideas of what will bring pleasure and pain, as formed by our education and judgment. Moreover, we tend to value our immediate desires over any long-term consideration. For both of these reasons, we often misjudge what is good for us in the long run.


Locke's terminology can be a little hard to follow here. To reiterate, a simple mode is a kind of complex idea built out of a simple idea. Like other modes, it is an attribute or quality that a substance can have, and not a substance in itself. The difference between a simple idea and a simple mode is perhaps best illustrated by considering colors. For Locke, individual colors, as recognized distinctly by the mind, are simple ideas. Thus, the mind has an idea of whiteness, redness, and so forth. The simple modes arising from these colors are "different degrees, or ... shades of the same color." So for Locke, there's a kind of prototypical idea of "redness" in the mind, and from that idea we get modes like "scarlet" and "crimson." It works similarly for other senses. We have simple ideas of, say, the tastes of coffee and steamed milk. But the taste of a latte would be a simple mode in Locke's taxonomy, formed by combining those two simple ideas.

The discussion of sensory phenomena is one place where Locke's theories invariably show their age. With colors, the problem is that Locke notices a subtle pitfall in the reasoning of others, yet he can't quite keep from falling into it himself. He rightly points out that people attach different, sometimes quite contradictory ideas to the same word, especially when abstract words like "justice" or "frugality" are used. (He'll have much more to say about this issue in Book 3, which is devoted to words and language.) He even notes in Book 2, Chapter 22 that various languages have words with no exact equivalent in English. Yet for Locke, none of this undermines the notion that there are certain simple ideas, more fundamental and immediate than all the rest. The trouble is, even these simple ideas vary from culture to culture. For instance, Locke sees "blue" and "yellow" as simple ideas, but "green" as a complex one. In Japanese, however, the same word is traditionally used for both colors. Does that make "green" a simple idea in Osaka, but a complex one in Oxford? Locke's ideas, even basic and seemingly uncontroversial ones, are the product of a specific cultural viewpoint. What's "obvious" to Locke isn't necessarily to be taken for granted.

Locke's treatment of volition in Chapter 21 is, in some respects, an end-run around the entire issue of free will. Rather than directly answer the question, he reframes it by attempting to define free. To be fair, the problem is not an easy one to begin with, and it becomes harder when you begin with the assumption that humans are morally responsible for their behavior. If humans are not in some sense free to choose their actions, there is no basis for the assignment of blame or praise, any more than we would blame a baseball for breaking a window. But for Locke, Christianity—with its concepts of moral accountability and final judgment—is non-negotiable. Thus, it would be extremely surprising if Locke did not find some room for freedom, and hence for morality, in his discussion of will. His solution is to admit that we cannot help willing things in the moment while insisting that we do have the freedom to question our desires.

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