An Essay Concerning Human Understanding | Study Guide

John Locke

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An Essay Concerning Human Understanding | Vol. 1, Book 2, Chapters 14–17 : Of Ideas | Summary



Vol. 1, Book 2, Chapter 14: Of Duration and Its Simple Modes

Locke proceeds to offer a categorization of "modes of duration" similar to the one he offered for "modes of space" in the previous chapter. Our ideas of succession and duration, he argues, come from our own observation of how our ideas come and go. Once we have these ideas, however, we can apply them even to intervals of time in which we are not present to observe, such as sleep. Locke suggests that despite all the different means of timekeeping, "the constant and regular succession of ideas in a waking man" is the proper measure of succession. In other words Locke sees time as a primarily subjective concept. Moreover, Locke points out that we cannot put two intervals of time next to one another the way we might with two physical objects. For him this implies that we can never really know that two intervals of time are equal. The chapter closes with a discussion of the concept of eternity, an idea Locke revisits in Chapter 17.

Vol. 1, Book 2, Chapter 15: Of Duration and Expansion, Considered Together

Locke observes that our ideas of duration and expansion (i.e., of time and space) have much in common: they can be subdivided into infinitely small pieces and stretch out to infinity. We even use familiar spatial metaphors to describe events in time—calling a moment a "point," for example. "Expansion and duration," he asserts, "do mutually embrace and comprehend each other; every part of space being in every part of duration, and every part of duration being in every part of expansion."

Vol. 1, Book 2, Chapter 16: Of Number

Now, Locke ventures a theory about the way in which our ideas of numbers arise. Unity, our idea of "one," is in Locke's view the simplest idea of them all. From it, he says, we create complex modes such "dozen" or "million" by simply sticking units together in our minds. Because these modes are so clearly distinct from one another (i.e., two is clearly not three, and 99 is clearly not 100), Locke regards ideas about number as the most precise and easy to distinguish. This, in his view, accounts for the clarity of mathematical proofs.

Vol. 1, Book 2, Chapter 17: Of Infinity

Building on the previous discussion of space and time, Locke ponders the origins of the idea of infinity. He points out that people have no trouble forming ideas of finite distances and finite timespans, and that there are no clear boundaries to either. In other words, there's no maximum unit of time or spatial distance. Despite this, Locke suggests, people have no "positive idea" of infinity, meaning they can't actually picture "infinity" in their minds. Instead, the concept of infinity is built on the realization that for any number, no matter how large, "one may yet go farther."


It may seem again as though Locke is splitting hairs in his enumeration of different types of ideas. But as the ideas under discussion grow more complicated, it becomes even more essential that Locke be able to trace them back to sensation and reflection. Locke's opponents, the nativists (those who view the mind as possessing innate ideas), might be perfectly willing to agree that some simple ideas (like the color red or the smell of a rose) arise only through experience. These ideas are directly related to sensory phenomena and are hard to separate from those phenomena. It would be difficult to argue that, say, a person with red-green colorblindness has distinct innate ideas of red and green. The nativist argument, however, is not an all-or-nothing proposition: unlike Platonic idealism (see Context), nativists in the early modern era usually accepted that some ideas are empirically acquired. Lockean empiricism, however, is an all-or-nothing proposition: it asserts that all ideas are experientially acquired, and none are innate. This means Locke is on the defensive, so to speak. For his empiricism to be justified, he must show that any idea—abstract or concrete, complicated or simple—can arise from experience.

Sometimes, as in his discussion of infinity (Chapter 17), Locke takes a roundabout route to this goal. It seems obvious, for instance, that nobody has ever directly experienced infinity in either space or time. Nobody, no matter how long-lived, can claim to have lived forever, and nobody's eyesight is sharp enough to see an infinite distance. Thus, at first glance, it seems that if the idea of infinity is to get into a person's head, it must come from some source other than experience. Not quite, says Locke. In his view, we don't have a "positive idea" of infinity to begin with. Instead, the idea of infinity is an extension, or perhaps a negation, of those finite ideas we do possess. An infinite distance is, for Locke, represented in the mind indirectly, as something longer than the longest distance we can think of. An infinite duration is something longer than the longest span of time we can conceptualize, even if we keep doubling that timespan in our minds. There is, in Locke's view, no mystery about how our finite ideas of time and distance arise, even when the quantities are extremely large. They first come about through sensation and are then extended through reflection, the two categories of experience which Locke admits.

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