1. LOCKE’S CAUSAL THEORY OF PERCEPTION
THE REALITY/APPEARANCE DISTINCTION SCIENCE NEEDS

2. JOHN LOCKE

3. Anti-Cartesianism/Rationalism
Rationalism (Descartes): some crucial concepts and truths are a priori and innate: mathematics - e.g., 1+ 2 = 3
logic - e.g., p, p q, therefore q
Empiricism (Locke): all concepts and truths are a posteriori, there are no innate ideas, the mind is a tabula rasa at birth.

4. (Des)Cartesian Presuppositions
Mind: immaterial substance (soul, spirit) which thinks (is conscious)
Body: material substance which does not think (is unconscious)
Perception: bodymind causation
idea/eidos – formal (immaterial) copy
Action: mindbody causation

5. Locke’s Definitions
i) IDEA = “Whatsoever the mind perceives in itself, or is the immediate object of perception, thought or
understanding”
ii) QUALITY = “the power to produce any idea in our mind”

6. Scientific appearance/reality distinction (paras. 9, 10, 23, 25)
Concerning Perception of Physical Objects
Reality = “Primary Qualities”
Qualities in object whether perceived or not
Appearance = “Secondary Qualities”
Qualities of “ideas” caused by perception
[You may ignore “tertiary qualities”]

7. 2 Kinds of Qualities of Objects
PRIMARY QUALITY SECONDARY QUALITY
i) essential not essential
ii) resembles idea does not resemble idea
iii) really in object nothing but power
(as in idea) (to produce idea)
Examples: Examples:
solidity, extension, colors, odors, figure, motion, flavors, sounds, number,… felt warmth,…

8. Arguments 1st Sort “steel dividing our flesh” argument
(para. 13, see also paras. 16, 17,18)
Evidence: some objects acting upon our sensory organs cause sensations (ideas), in particular pain or pleasure which do not resemble the object.
Conclusion: sensations (percepts) need not resemble objects (so are secondary).
Note: for Locke, Descartes, Newton, Galileo, etc., representation is a function of resemblance.

9. Arguments 2nd Sort removal of senses argument (para. 17)
Premise: objects do not depend on our senses to exist.
Premise: essential qualities remain when objects not perceived.
Conclusion: primary qualities are essential, secondary qualities are accidental

10. “manna” argument (paras. 17, 18)
Arguments 3rd Sort
“manna” argument (paras. 17, 18)
NOTE: Manna was a brand-name laxative which doctors like Locke bought in bulk and cut up into smaller pieces for their patients.
Secondary Qualities: mere appearance
The color of the bit of manna is not in it but in our percept (idea) of it—just like the pains it causes.
Primary Qualities: must be real
“…a circle or square are the same, whether in idea or existence, in the mind or in the manna…”

11. Arguments 4th Sort
microscopic processes argument (paras. 13, 14, 17, 2, …)
Corpuscularian (atomic) theory: the colors, odors, flavors of bodies are ideas produced in our minds by microscopic processes of those bodies interacting with our sensory organs and nervous systems.
But God could have joined (“annexed”) other ideas to those very same motions in our sensory organs and nervous systems

12. Arguments 5th Sort porphyry [non-essential change](para. 19)
Also: necks of pigeons, colors of clouds, etc.
Porphyry is a stone that changes its color and patterns of white sparkles depending on how it is turned in the light.
But surely the porphyry itself is not changing in this process.
So: only our perceptual ideas are changing, so color is a secondary quality.

13. Arguments 6th Sort Secondary quality inconsistencies (para 21)
Method: Cool one finger by holding it in cold water, warm another finger by holding it in hot water, then put both fingers in lukewarm water.
Observation: water feels warm to one finger, cool to the other.
But: impossible for water to be both warm and cold
Conclusion: both the sensation of warmth and the sensation of cold are secondary (illusory).