54 pages 1 hour read

John Locke

An Essay Concerning Human Understanding

Nonfiction | Book | Adult | Published in 1690

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Summary and Study Guide


An Essay Concerning Human Understanding by John Locke is a study of how humans think, learn, and retain knowledge. Scholars often focus first on Locke’s philosophical treatises, but his work on epistemology complements and shapes his political thought. Born in 1632, the English philosopher ushered in the Age of Enlightenment and is considered one of the greatest Western philosophers in history. An Essay Concerning Human Understanding, first published in 1690, explores the origin and nature of knowledge. Locke’s work is unique because it rejects the previously accepted concept of innate knowledge and advocates for reason and observation.

This guide references the 2014 Wordsworth Classics edition, which also includes Locke’s Second Treatise of Government.


Locke’s An Essay Concerning Human Understanding details the 17th-century philosopher’s exploration of the origin and scope of human knowledge. Locke’s work challenges previously accepted ideas about innate knowledge—the idea that certain principles are present in the minds of all humans at birth. Innate knowledge is supported by the notion of universal consent, which Locke vehemently challenges. Instead, Locke asserts that the origin of knowledge is sensory experience. As humans grow up and accumulate experiences, intaking sensory details, they form ideas and principles about the world around them. They apply different processes of thinking to make sense of the ideas and to find patterns. By connecting and comparing ideas, humans form complex and abstract thoughts.

Locke argues that observation and sensory experience are the first steps to an intellectual life. This empiricist approach emphasizes reason, solidifying Locke as a key figure in Enlightenment thinking, which championed logic and science. In An Essay Concerning Human Understanding, Locke advocates for the concept of tabula rasa. This theory proposes that the mind is a blank slate that experience fills over time. The book contextualizes the following themes: The Tabula Rasa Theory, Empiricism and the Role of Experience, and The Spiritual Nature of Knowledge. These themes work together to form a full picture of Locke’s epistemological philosophy. The work includes a brief introduction and four books.

In Book 1, “Of Innate Notions,” Locke outlines his three goals: to discover the origin of ideas, to understand the nature of an idea, and to determine how to acquire knowledge when it seems limited. Locke challenges earlier schools of philosophy and the concept of innate knowledge. He denies the existence of universal consent, claiming that no singular principle exists on which all humans can agree. Instead, ideas form through experience. While asserting that God plays a vital role in the acquisition of knowledge, Locke denies that God imparts innate knowledge or that morality and the concept of God are divinely appointed to the mind before birth.

In Book 2, “Of Ideas,” Locke explores simple and complex ideas. He argues that two types of experience contribute to ideas: sensation and reflection. Sensory impressions reveal simple ideas. As humans gather sensory impressions and then compare and align ideas with other ideas, understanding becomes complex and nuanced. Locke asserts that the human mind is distinct from its animal counterparts because it can make judgments, discern, compare, compose, and form abstract thoughts. The ability to apply these thought processes, Locke suggests, reflects God’s nature; furthermore, God imparts pain and pleasure to help humans determine the difference between right and wrong.

Book 3, “Of Words,” breaks down abstract ideas and navigates the relationship between language and ideas. Producing names for every individual idea would present a formidable challenge. Therefore, classification provides the clarity and conciseness to bring order to ideas. Additionally, Locke explores the subject of essences, a concept widely accepted since Plato. Locke proposes that essences are general ideas about the things that humans observe. He distinguishes real essences from nominal essences, which represent the abstract. This book finishes with a critique of language. Locke reveals how the impreciseness of language complicates philosophy and science. He therefore challenges scientists and philosophers to avoid misuse of language. Those who use words inconsistently or without fully understanding the ideas they represent contribute to the confusion of language and ideas. Locke proposes several remedies, including using the same words for specific ideas and taking the opportunity to define meaning.

Book 4, “Of Knowledge and Probability,” addresses the nature of knowledge. Locke shows how finding the ways in which ideas relate and diverge contributes to an understanding of truth and probabilities. Sensory experience is the source of knowledge but can limit understanding. Humans are unable to know more things with certainty because of their own restrictions. However, they can understand the nature of existence. People recognize their own existence through intuition, the existence of God through perception, and the existence of others through sensory experience. Locke challenges the idea that a world outside the mind doesn’t exist, citing human experience as substantial evidence. In addition, he also shows the relationship between faith and reason, arguing that the two inform and complement one another.

Locke concludes by encouraging his readers to take up the banner of knowledge. Only by loving knowledge and actively and intentionally pursuing it will humans be able to inch closer to certainty and truth. Locke’s advocacy for thinking and contemplation reflects a history of epistemology that emphasizes the noble pursuit of understanding.

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