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The philosopher who famously posed the problem of explaining color to a blind person—or more accurately, argued that a person born blind could never truly understand color—was the 17th-century English philosopher John Locke. [1]
Locke argued that because all knowledge comes from sensory experience, a person who has never seen cannot grasp the concept of color, as they lack the necessary sensory input. [1, 2]
Key Aspects of the Historical Context:
- The Argument: Locke (in his An Essay Concerning Human Understanding, 1689) used a blind person's inability to conceptualize "red" or "scarlet"—famously associated by a blind scholar named John Troughton with the sound of a trumpet—to demonstrate that color is a "secondary quality" requiring visual experience.
- Related Thought Experiment: Locke was closely associated with William Molyneux, who posed a related, famous thought experiment known as "Molyneux's Problem." This question asks whether a person born blind, who can identify a sphere and a cube by touch, could distinguish them by sight alone if they were suddenly given the ability to see.
- Modern Relevance: This philosophical problem is frequently discussed in modern cognitive science, with studies in 2021 from Johns Hopkins University challenging Locke’s assumption by showing that blind individuals can understand color concepts similarly to sighted people through language and social learning. [1, 2, 3, 4, 5]
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John Troughton (1637–1681) was a blind Nonconformist minister and fellow student with the philosopher John Locke (1632–1704) at Oxford University. Troughton’s struggles to understand Biblical imagery and sensory experience likely stimulated Locke’s thoughts on epistemology, particularly regarding how humans gain knowledge without sight, influencing Locke's foundational empiricist works. [1, 2]
Key Connections:
- Oxford Connection: Both studied at Oxford, where Troughton was known as a brilliant but blind scholar, potentially influencing Locke's questioning of how knowledge is acquired, according to research shared on ResearchGate.
- Empiricism (tabula rasa): Locke’s idea that the mind is a blank slate (\(tabula\) \(rasa\)) that gains knowledge through experience (sensory data) may have been influenced by observing Troughton's sensory-based perception, a connection explored in academic studies.
- John Locke's Legacy: Locke, considered the "Father of Liberalism," developed theories of natural rights (life, liberty, property) and social contract that influenced the American Revolution, as described in biographies by Britannica and the American Battlefield Trust. [1, 2, 3, 4]
About the Individuals:
- John Locke (1632–1704): A central figure in the Enlightenment, his Essay Concerning Human Understanding (1689) argued against innate ideas, while his Two Treatises of Government (1690) defended democratic principles and the right to revolution.
- John Troughton (1637–1681): A prominent Puritan, nonconformist minister who was blinded by smallpox at age four, yet became a respected academic at Oxford, challenging peers with his intellectual capacity despite his disability, according to discussions on Reddit. [1, 2, 3, 4]
Troughton is considered a possible inspiration for Locke’s intellectual journey into how sensory perception shapes human understanding. [1]
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The "John Troughton problem" refers to a historical instance that likely inspired John Locke's philosophical argument about whether sensory concepts can be understood without direct experience. [1]
John Troughton was a 17th-century nonconformist minister and scholar who went blind from smallpox at a young age. He was a contemporary of Locke at Oxford University. [1, 2, 3]
The Core of the Problem
The "problem" is illustrated by an anecdote in Locke's An Essay Concerning Human Understanding regarding a "studious blind man" (widely believed to be Troughton) who claimed he finally understood the color scarlet. When asked what scarlet was like, the man answered that it was "like the sound of a trumpet". [, 2]
Locke used this to argue that:
- Knowledge requires experience: A blind person can learn the word "scarlet" and its associations (e.g., that it is "vivid" or used in royal imagery), but they cannot truly understand the idea or "simple sensation" of the color itself.
- The failure of analogy: Comparing a color to a sound (a form of synesthesia-like association) demonstrates that the blind man was merely substituting one sensory category for another rather than grasping the visual concept. [, 3]
Why It Matters
This case is a foundational example of Empiricism, the theory that the mind is a tabula rasa (blank slate) and all ideas originate in sensory experience. It suggests that no amount of verbal explanation or definition can ever give a person the "simple idea" of a sensation they have not personally experienced. [1, 2]
Would you like to know how modern neuroscience studies from institutions like Johns Hopkins University have recently challenged Locke's long-standing conclusion?
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John Locke believed that because true knowledge stems from sensory experience, a blind person cannot truly understand color, but modern research shows blind individuals conceptualize color similarly to sighted people. They do this through language, social context, and inference, understanding that objects have colors and associating them with temperature (e.g., warm/red vs. cold/blue). [1, 2, 3]
Key Perspectives on Blindness and Color Knowledge:
- Locke's Philosophical View: In his "An Essay Concerning Human Understanding," Locke proposed that if a person lacks a sense (like sight), they cannot form the corresponding ideas (like color). He famously noted that a blind person has no notion of color and argued that trying to describe color to them is essentially pointless.
- The "Scarlet Sound" Example: Locke recalled a story about a blind man who attempted to understand "scarlet" by comparing it to the sound of a trumpet, which modern commentators often view as an early example of synesthesia.
- Modern Cognitive Science Approach: Recent studies from Johns Hopkins University have challenged Locke's view, finding that people who are congenitally blind understand color concepts (such as "bananas are yellow") just as well as sighted individuals. They learn this through conversations and language, allowing them to form an in-depth understanding rather than just shallow, arbitrary facts.
- Inference Over Memory: Rather than remembering visual images, blind individuals use "knowledge of the world" to infer colors based on taxonomy and habitat—for example, knowing that an animal is a mammal and therefore likely to be brown or gray. [1, 2, 3, 4, 5, 6]
While they do not experience the visual sensation, blind individuals understand color as a coherent system linked to objects, functions, and categories. [1, 2, 3, 4, 5]
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Jean le Rond d’Alembert did address the philosophical problem of explaining sensory experience to the blind, primarily within the context of Empiricism and the Enlightenment's fascination with the "science of man."
While he may not have used the specific name "John Troughton"—as Locke's anecdote of the "studious blind man" was often discussed as a general case in French circles—d'Alembert engaged with the underlying problem in several ways: [1]
- Empiricist Framework: In his Preliminary Discourse to the Encyclopédie (1751), d'Alembert defended the sensory origins of knowledge, a core Lockean principle. He argued that our ideas are generated through the senses, which inherently implies that a missing sense (like sight) creates a fundamental gap in a person's conceptual "storehouse" of the universe.
- The Molyneux Problem: D'Alembert was deeply familiar with Molyneux’s Problem, which was the primary vehicle through which Locke’s ideas about blindness were debated in France. D'Alembert, alongside contemporaries like Denis Diderot (who wrote the famous Letter on the Blind), explored how the lack of sight would reshape a person's entire logical and mathematical understanding.
- Materialism and Sensation: In the Conversation between d'Alembert and Diderot, he discusses the transition from a "sentient being" to a "thinking being," exploring how consciousness is founded on memory and sensory reflection. This dialogue reflects the era's broader attempt to solve the "John Troughton problem" by determining if reason could bridge the gap where direct sensation is missing. [1, 2, 3, 4, 5]
D'Alembert generally aligned with the view that while a blind person could use analogy (like the "trumpet" comparison) to understand the social or functional role of color, they could never possess the "simple idea" or raw sensation of the color itself. [1, 2, 3]
Would you like to explore Diderot’s more radical take on this in his Letter on the Blind, which directly challenged many of these Lockean assumptions?
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Denis Diderot’s Letter on the Blind (1749) was a landmark response to the empiricist tradition established by Locke and d'Alembert. While Diderot does not mention John Troughton by name, his entire essay is a direct challenge to the idea that a blind person’s understanding of the world is inherently "deficient" or merely an exercise in failed analogy like the "trumpet" comparison. [1, 2]
Diderot’s radical approach turned the problem on its head by arguing that blindness isn't just a lack of information, but a different way of being that provides unique insights into reality. [1, 2]
1. Re-defining Sensory Success
Instead of focusing on a blind man’s "failure" to grasp scarlet, Diderot highlights the "success" of Nicholas Saunderson, a blind mathematician who taught optics and the theory of light at Cambridge. [1, 2]
- Optics without Sight: Diderot points out that Saunderson could explain the behavior of light rays and lenses using only geometry and touch.
- Abstract Thought: He argued that the blind might actually be better at abstract thinking (like math) because they are not distracted by the "noise" of visual appearances, which often deceive the sighted. [, 2]
2. The "Hand as an Eye"
Diderot interviewed a blind man from Puiseaux who famously described a mirror as an object that "sets things in relief at a distance from themselves". []
- Diderot was amazed by this definition, noting that even a sighted genius like Descartes would have been proud of it.
- This suggested that the blind could arrive at accurate conceptual truths through different sensory paths, rather than just being "blind" to the truth. [, 3]
3. The Moral and Social Critique
Diderot used the blind person’s perspective to criticize established social and religious norms: [1, 2, 3]
- Atheism: He suggested that because a blind person cannot see the "order" of the cosmos, they might be naturally inclined toward atheism, as they cannot perceive the visual "proofs" of a creator.
- Morality: He argued that a blind person's morality is based on tangible harm (like theft) rather than visual modesty (like nakedness), showing that our values are often shaped by our specific senses rather than universal truths. [, 2]
4. Direct Response to Locke
While Locke saw the "trumpet" analogy as proof of a fundamental gap in knowledge, Diderot viewed it as proof of the interconnectedness of all human perception. He believed that the different senses are ultimately just different ways for the same mind to organize the same physical reality. [1, 2, 3]
Would you like to see how modern research from Johns Hopkins supports Diderot's intuition that the blind can have a deep, structural understanding of color?
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