Primary and secondary qualities

A philosophical distinction between qualities thought to belong to objects independently of perception and qualities arising through their effects on perceivers.

John Locke: An English philosopher whose empiricism and account of ideas shaped modern debates about knowledge and perception. He gave the distinction its influential early modern formulation in An Essay Concerning Human Understanding.
Corpuscularianism: The theory that material bodies consist of tiny particles whose arrangements and motions explain observable properties. Locke uses corpuscular structure to explain how bodies produce sensory ideas.
George Berkeley: An Irish philosopher who argued that sensible objects consist in ideas perceived by minds. Berkeley rejects primary qualities as independent of perception, applying his critique to both kinds.
Color realism: The view that colors are real properties of objects, rather than features constituted solely by experience. Color tests whether a quality can be objective while depending on how visual systems respond.
Substance: A basic entity understood to exist in its own right and bear properties. Locke treats qualities as powers or features grounded in material substance.
Primary quality: A quality, such as shape or motion, held to belong to a body independently of observers. These are the object-side qualities that Locke says ideas resemble.
Thomas Reid: A Scottish philosopher who defended common-sense realism and direct perception of the external world. Reid challenges the representational framework that makes the distinction seem necessary.
Color subjectivism: The view that colors depend substantially on perceivers or their sensory experiences. It develops the thought that color belongs to the perceiver's experience rather than the object alone.
Perception: The processes by which organisms acquire and interpret information through their senses. The distinction asks which perceived features belong to objects and which depend on perceivers.
Secondary quality: A power of an object to produce sensations such as color, taste, or sound in perceivers. These qualities name object-based powers whose effects do not resemble the sensations they cause.

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