Locke on the Human Understanding: The Origin of Ideas

John Locke’s Essay Concerning Human Understanding (1689) is one of the foundational texts of the modern empiricist tradition. The book develops a comprehensive account of the origin, the scope, and the limits of human knowledge, and it set the agenda for the subsequent development of the British empiricist tradition. This article examines the central arguments of the Essay, including the rejection of innate ideas, the sources of ideas, and the limits of human knowledge.

The Rejection of Innate Ideas

The Essay opens with a rejection of the doctrine of innate ideas. The doctrine, which had been defended by various rationalist philosophers, held that the human mind is born with certain ideas or principles already in it, and that these ideas are the foundation of human knowledge.

Locke argues that there are no innate ideas, either in the speculative realm (ideas of God, of identity, of substance) or in the practical realm (principles of morality). The mind, he argues, is a “blank slate” (tabula rasa) at birth, and all knowledge comes from experience.

Locke supports this claim with several arguments. First, if there were innate ideas, they would be present in all human beings, including children and idiots. But it is clear that children and idiots do not have the same ideas as adults, and the absence of these ideas in children and idiots shows that the ideas are not innate.

Second, if there were innate ideas, they would be universally accepted. But there are no ideas that are universally accepted, and the diversity of human opinions shows that the ideas are not innate.

Third, even if there were universal agreement on certain ideas, this would not show that the ideas are innate. Universal agreement could be explained by the universal experience of certain facts, such as the fact that fire burns or that pleasure is agreeable. The universality of these agreements is not evidence of innateness.

The Sources of Ideas

Locke argues that all ideas derive from two sources: sensation and reflection.

Sensation is the source of ideas of the external world. Through the senses, we perceive colors, sounds, textures, shapes, and the various other qualities of the objects around us. The ideas of sensation are the materials of our knowledge of the external world.

Reflection is the source of ideas of the operations of our own minds. Through reflection, we perceive our own thinking, doubting, willing, and the various other operations of our minds. The ideas of reflection are the materials of our knowledge of the inner world of our own minds.

All complex ideas, including ideas of substance, of identity, of cause and effect, and of moral and mathematical truths, are derived from these simple ideas by various operations of combination, comparison, and abstraction. The mind is thus the active source of the complex ideas, even though the materials of the ideas are derived from experience.

The Primary and Secondary Qualities

One of the most important contributions of the Essay is the distinction between the primary and the secondary qualities of objects. The distinction is a development of the mechanistic philosophy of the seventeenth century, and it has had a profound influence on the development of the modern scientific worldview.

The primary qualities are the properties of objects that the objects have in themselves, independent of being perceived. The primary qualities include solidity, extension, figure, motion, and number. These qualities produce the same ideas in all observers, regardless of the conditions under which the objects are perceived.

The secondary qualities are the properties of objects that depend on the interaction between the objects and the sense organs of the observer. The secondary qualities include color, sound, taste, and smell. These qualities do not produce the same ideas in all observers, and the ideas depend on the conditions under which the objects are perceived.

The distinction was an important contribution to the development of the modern scientific worldview. The natural sciences, in the modern period, have focused on the primary qualities of objects, and they have generally treated the secondary qualities as the result of the interaction between the primary qualities and the sense organs of the observer.

The Limits of Human Knowledge

Locke was aware that his empiricist account of the origin of ideas had important implications for the limits of human knowledge. He distinguished among three kinds of knowledge: intuitive knowledge, demonstrative knowledge, and sensitive knowledge.

Intuitive knowledge is the immediate perception of the agreement or disagreement of ideas. For example, when we perceive that white is not black, or that three is more than two, we have intuitive knowledge. Intuitive knowledge is the most certain kind of knowledge, and it is the foundation of all other kinds of knowledge.

Demonstrative knowledge is the perception of agreement or disagreement through a chain of reasoning. For example, when we prove that the sum of the angles of a triangle is 180 degrees, we have demonstrative knowledge. Demonstrative knowledge is less certain than intuitive knowledge, but it is still a kind of knowledge.

Sensitive knowledge is the perception of the existence of particular external objects. For example, when we see the sun, we have sensitive knowledge of the existence of the sun. Sensitive knowledge is the least certain of the three kinds of knowledge, and it is based on the observation of the agreement of our ideas with the actual existence of the external objects.

Beyond these three kinds of knowledge, Locke argued, there were many important questions that human beings could not answer with certainty. He was particularly skeptical of the claims of traditional metaphysics, and he argued that the existence of God, while it could be established by a kind of demonstrative reasoning, was not susceptible to the kind of proof that metaphysical philosophers had claimed.

The Influence of the Essay

The Essay has had a profound influence on the development of modern philosophy. The book set the agenda for the British empiricist tradition, and it provoked responses from the rationalist philosophers, the Kantian philosophers, and the various other philosophical traditions that developed in the centuries since.

The most important immediate influence of the Essay was on the development of the British empiricist tradition. George Berkeley developed an idealist critique of Locke’s distinction between primary and secondary qualities, and David Hume pushed the empiricist position to skeptical conclusions. The work also had a profound influence on the development of the modern natural sciences, which were based on the careful observation of natural phenomena and the systematic collection of natural facts.

Further Reading

• The Stanford Encyclopedia of Philosophy (plato.stanford.edu), relevant entry
• The Cambridge Companion to [Thinker] (Cambridge University Press)
• Isaiah Berlin, Four Essays on Liberty (1969)