An Essay Concerning Human Understanding

Ideas fall into two categories: simple and complex. Different senses produce different ideas. For example, one may touch and see an object, such as an ice cube, but the information received between the two senses is divergent. Once the mind applies reflection to simple ideas, it can find patterns and create categories. Humans intake simple and complex ideas through sensory experience. Locke suggests that humans are unique because God has instilled in them many senses to help them understand the world. Additionally, Locke proposes that in addition to the five senses, other sense types may exist that have not yet been identified.

Locke proposes four ways in which an idea enters the mind: through one sense only, through more than one sense, through reflection, and through all sensation and reflection. This chapter focuses on the first type. Light, color, noise, taste, and simple touch—such as hot or cold, solid or liquid—convey singular ideas to the brain.

The most constant form of sense perception is solidity. Humans feel this sensation through the resistance of an object. Locke adds that an interchangeable word may be “impenetrability,” but solidity provides a clearer representation of the sense he describes. Solidity differs from space, which allows the mind to conceive of other physical objects separate from the body. In addition, solidity differs from hardness because its impassable qualities block the body from other objects. For example, a football, although not hard, is solid because it stops the hand from touching the air inside.

In contrast to simple ideas through one sense, some ideas come through multiple senses. Locke identifies these as “space or extension, figure, rest, and motion.” These ideas leave impressions on more than one bodily sense.

Like ideas that come through sensory perception, ideas that come through reflection fall into two categories. This chapter defines the actions of the first type of simple ideas through reflection alone. This concept is further divided into two classes: “Perception, or Thinking; and Volition, or Willing” (119). Locke provides the overarching names “understanding” and “will” for these classes, which contribute to important actions such as discerning and believing.

Both sensation and reflection contribute to simple ideas about concepts like pleasure, pain, and existence. Locke suggests that most thoughts produce either pleasure or pain and that this is an imparted perception to help individuals distinguish between good and bad thoughts and actions. The desire to pursue pleasure and avoid pain provides instruction on what is right or wrong. Excessive sensory input, such as too much light, emphasizes the importance of moderation.

The senses produce positive ideas in the mind; however, Locke distinguishes between an idea and understanding. As an example, he cites the colors white and black. He suggests a difference between perceiving these two colors and understanding the science behind their appearances. Ideas form through the simple intake of sensory experience; for example, a snowball presents simple concepts such as “cold” and “white.” Qualities help individuals put different senses together to create new ideas within the mind. In this way, the mind creates the concept of a “snowball” as a collection of sensory experiences.

Locke then concludes that unseen bodies of motion must transmit the messages of sensory experience from an object to the mind. The mind separates the qualities into primary and secondary categories. Primary qualities produce singular sensory impressions. Secondary qualities produce more than one sensory impression. These qualities exist within the body of an object and in the mind of the person perceiving them. Primary qualities include “figure” and “number.” Secondary qualities are those that combine multiple colors or sounds. A third type of quality, “powers,” can change a sensory impression. For example, the sun can melt wax and turn it white.

Although perception can happen only when a person is awake, the brain process functions beneath the radar. Locke suggests that perception is passive, while reflection is an action of focus and intention. Babies may engage in perception before their birth and develop certain simplistic ideas based on sensory input, such as warmth or hunger. However, this differs from the concept of innate knowledge. Locke argues that all animals can perceive in varying degrees. This, he concludes, is a way for God to exist in all living things. Humans are unique in the animal world because they go a step further and make judgments about their perceptions, allowing them to find patterns and refine their ideas.

Beyond perception and judgment is retention. The human mind intakes ideas and uses perception to make sense of them; the holding of these ideas and the ability to conjure them are components of retention. Pleasure and pain help solidify memory. Repetition also aids retention, either through repeated sensory experience or recall of an idea. Memory is essential to perception and judgment; without it, humans would be unable to use evidence outside what is available in the moment. However, memory comes with defects: Ideas are lost, and the brain’s functioning often moves slowly.

In addition to perception, judgment, and retention, the human mind is unique in its ability to use discernment. Drawing distinctions and making shrewd choices uses a separate set of intellectual skills than making witty remarks. Clever people are faster at recalling and putting ideas together. Discernment requires a separate skill: to separate ideas and examine their parts.

Locke then briefly outlines three other abilities of the mind: comparing, composition, and abstracting. He argues that comparison may be a skill available only to humans because comparison is necessary only for abstraction. “Composition” is the combining of simple ideas into complex ones. Locke calls this concept “enlarging.” The capacity to intake many objects and group them into categories that represent a larger idea is “abstraction.” This completes the functions of the passive mind toward simple ideas.