An Essay Concerning Human Understanding

by John Locke
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Last Updated on October 26, 2018, by eNotes Editorial. Word Count: 1282

John Locke’s purpose in An Essay Concerning Human Understanding is to inquire into the origin and extent of human knowledge. His conclusion—that all knowledge is derived from sense experience—became the principal tenet of empiricism, which has dominated Western philosophy ever since. Even George Berkeley, who rejected Locke’s distinction between sense...

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John Locke’s purpose in An Essay Concerning Human Understanding is to inquire into the origin and extent of human knowledge. His conclusion—that all knowledge is derived from sense experience—became the principal tenet of empiricism, which has dominated Western philosophy ever since. Even George Berkeley, who rejected Locke’s distinction between sense qualities independent of the mind and sense qualities dependent on the mind, produced his idealism in response to Locke’s provocative philosophy and gave it an empirical cast that reflected Western culture’s rejection of innate or transcendental knowledge.

An Essay Concerning Human Understanding is divided into four books: book 1, “Of Innate Notions”; book 2, “Of Ideas”; book 3, “Of Words”; and book 4, “Of Knowledge, Certain and Probable.”

In preparation for his radical claim that all ideas are derived from experience, Locke begins his essay with a careful consideration of the thesis that there are innate ideas. Locke first examines the notion that there are ideas that are a necessary part of human understanding and are, therefore, common to all people. Locke’s attack on this thesis is from two directions. He argues that many of the ideas that are supposed to be innate can be and have been derived naturally from sense experience, that not all people assent to those ideas that are supposed to be innate. Locke maintains that even if reason enables people to discover the truth of certain ideas, those ideas cannot be said to be innate, for reason is needed to discover their truth.

In book 2, “Of Ideas,” Locke considers the origin of such ideas as those expressed by the words “whiteness,” “hardness,” “sweetness,” “thinking,” “motion,” “man,” and the like. The second section states his conclusion: Let us then suppose the mind to be, as we say, white paper void of all characters, without any ideas. How comes it to be furnished? . . . Whence has it all the materials of reason and knowledge? To this I answer, in one word, from experience. . . . Our observation, employed either about external sensible objects, or about the internal operations of our minds perceived and reflected on by ourselves, is that which supplies our understandings with all the materials of knowledge.

The two sources of ideas, according to Locke, are sensation and reflection. By the senses people come to have perceptions of things, thereby acquiring the ideas of yellow, white, or cold, for example. Then, by reflection, by consideration of the mind in operation, people acquire the ideas of thinking, doubting, believing, knowing, willing, and so on.

By sensation people acquire knowledge of external objects; by reflection people acquire knowledge of their own minds. Ideas that are derived from sensation are simple; that is, they present “one uniform appearance,” even though a number of simple ideas may come together in the perception of an external object. The mind dwells on the simple ideas, comparing them to one another, combining them, but never inventing them. By a “simple idea” Locke means what some modern and contemporary philosophers have called a “sense-datum,” a distinctive, entirely differentiated item of sense experience, such as the odor of some particular glue or the taste of coffee in a cup. He calls attention to the fact that people use sense experience to imagine what they have never perceived, but no operation of the mind can yield novel simple ideas.

By the quality of something, Locke means its power to produce an idea in someone sensing the thing. The word “quality” is used in the essay in much the same way the word “characteristic” or “property” has been used by other writers. Locke distinguishes between primary and secondary qualities. Primary qualities are those that matter has constantly, whatever its state. As primary qualities Locke names solidity, extension, figure, motion or rest, and number. By secondary qualities Locke means the power to produce various sensations that have nothing in common with the primary qualities of the external objects. Thus, the power to produce the taste experience of sweetness is a secondary quality of sugar, but there is no reason to suppose that the sugar itself possesses the distinctive quality of the sensation. Colors, tastes, sounds, and odors are secondary qualities of objects. Locke also refers to a third kind of quality or power, called simply “power,” by which he means the capacity to affect or to be affected by other objects. Thus, fire can melt clay; the capacity to melt clay is one of fire’s powers, and such a power is neither a primary nor a secondary quality.

Locke concludes that primary ideas resemble external objects, but secondary ideas do not. It is this particular claim that excited other professional philosophers, with Berkeley arguing that primary qualities can be understood only in terms of human sensations, so that whatever generalization can be made about secondary qualities would have to cover primary qualities as well, and with other philosophers arguing that Locke had no ground for maintaining that primary ideas “resemble” primary qualities, even if the distinction between primary and secondary qualities is allowed.

Complex ideas result from acts of the mind, and they fall into three classes: ideas of modes, of substances, and of relations. Modes are ideas that are considered to be incapable of independent existence since they are affections of substance, such as the ideas of triangle, gratitude, and murder. To think of substances is to think of “particular things subsisting by themselves,” and to think in that manner involves supposing that there is a support, which cannot be understood, and that there are various qualities in combination which give various substances their distinguishing traits. Ideas of relations are the result of comparing ideas with each other.

After a consideration of the complex ideas of space, duration, number, the infinite, pleasure and pain, substance, relation, cause and effect, and of the distinctions between clear and obscure ideas and between true and false ideas, Locke proceeds to a discussion, in book 3, of words and essences. Words are signs of ideas by “arbitrary imposition,” depending upon observed similarities that are taken as the basis for considering things in classes. Words are related to “nominal essences,” that is, to obvious similarities found through observation, and not to “real essences,” the actual qualities of things. Locke then discusses the imperfections and abuses of words.

In book 4, Locke defines knowledge as “the perception of the connection of and agreement, or disagreement and repugnancy, of any of our ideas.” An example cited is one’s knowledge that white is not black, Locke arguing that to know that white is not black is simply to perceive that the idea of white is not the idea of black.

Locke insists that knowledge cannot extend beyond the ideas one has, and that people determine whether ideas agree or disagree with each other either directly, by intuition, or indirectly, by reason or sensation. Truth is defined as “the joining or separating of signs, as the things signified by them do agree or disagree one with another.” For example, the proposition “White is not black” involves the separation by “is not” of the signs “white” and “black,” signifying the disagreement between the ideas of white and black; since the ideas are different, the proposition is true. Actually to have compared the ideas and to have noted their disagreement is to know the fact that the true proposition signifies.

Locke devotes the remaining chapters of book 4 to arguing that people have knowledge of their existence by intuition, of the existence of God by demonstration, and of other things by sensation. Here the influence of René Descartes is clearly evident. It is the empiricism of the earlier parts of the book that won for Locke the admiration of philosophers.

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