Khalifa
Brock and Mares Ch.4: Idealism
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Background
A. Idealism
General idea: nothing exists except minds and ideas in minds.
Subjective idealism: individual human minds perceive nothing but themselves and their own
ideas.
Absolute idealism: everything, including individual human minds, is part of a greater mind:
the mind of God.
B. Idealism as anti-skeptical
If subjective idealism is true, then only our minds and ideas exist.
We can know everything about our minds and our ideas.
So, if subjective idealism is true, then we can know everything that exists.
If we can know everything that exists, then skepticism is false.
So, if subjective idealism is true, then skepticism is false.
II.
Locke
A. Locke’s representational realism
We are not directly aware of physical objects, only our representations/ideas of them.
B. Representation & reality
Physical objects are rather unlike our representations/ideas of them.
Primary qualities (e.g. size, shape, movement, and solidity) are properties that objects
have in and of themselves.
Secondary qualities (e.g. color, odor, taste) are properties only of our representations of
things; they aren’t properties that objects have in and of themselves.
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Berkeley’s theory of ideas
A. Imagism and abstract ideas
Abstract ideas are indeterminate; they’re ideas of things without being determined in all
of their properties.
a. Abstract ideas: ideas about kinds of things, but not of particular things.
i. Ex. Triangle, dog, human
All ideas are mental images (= imagism).
We cannot have mental images of things that are no fully determinate.
We do not have any abstract ideas.
B. More on imagism
For Berkeley, to understand that something is F is to imagine a particular thing that is F.
(This is the principle of specification, PS)
o More precisely: If S understands that there is some x that is F, then there is some x
such that S imagines that x is F.
IV.
Berkeley on primary & secondary qualities
A. Big Picture
B1. The statement “The physical world in itself contains no secondary properties” is
meaningless.
B2. We cannot accept any theory that contains meaningless statements.
B3. So we cannot accept any theory that contains the statement, “The physical world in itself
has no secondary properties.”
Khalifa
Brock and Mares Ch.4: Idealism
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B. Berkeley’s argument for B1
1. If a statement that p is meaningful, then it expresses the idea that p.
2. So if the statement “The physical world in itself contains no secondary properties” is
meaningful, then it expresses the idea that the physical world in itself contains no
secondary properties, i.e. of a colorless, tasteless, etc. world consisting only of shapes,
motion, etc.
3. All ideas are mental images (imagism, again).
4. We cannot have a mental image of a physical world that in itself contains no secondary
properties.
B1. The statement “The physical world in itself contains no secondary properties” is
meaningless.
V.
Conceptual realism & idealism
A. Big Picture
C1. Conceptual realism: if it’s inconceivable/unimaginable that p, then not-p.
C2. It’s inconceivable/unimaginable that any physical object exists without having secondary
qualities.
C3. So, no physical object exists without having secondary qualities.
C4. Secondary qualities cannot exist except in minds.
C5. So, no physical object exists except in minds.
B. Argument from relativity for C4
R1. An object can have different secondary qualities depending on one’s perspective.
R2. Different species perceive things to have different secondary qualities.
R3. An individual can perceive different secondary qualities in different circumstances.
R4. The best explanation for all of this variability/relativity in the perception of secondary
qualities is that they cannot exist except in our minds.[probably]
C4. So, secondary qualities cannot exist except in our minds.
C. A challenge to R4
 An alternative explanation of the variability/relativity in the perception of secondary
qualities is that some of these perceptions are inaccurate.
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Berkeley’s master argument
A. The simple version
Hylas conceives that there is something that is unconceived.
Hylas is conceiving of something as being both conceived and unconceived
B. Problem with the simple version
It’s invalid: the premise can be true when the conclusion is false:
Suppose that S conceives that something is red.
a. Here, that something is red is the content of S’s representation.
S’s conception that something is red need not itself be red.
a. A “red conception” is weird. Here S’s conception is the way that the red thing is
represented to S.
Similarly, Hylas’ conceiving that something is unconceivable (content) doesn’t mean that his
conception (way of representing) is unconceivable.
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Brock and Mares Ch.4: Idealism
C. The modal version: background
Possible worlds: a term of art used by logicians to denote distinct possibilities.
Principle of possibility (PP): If it’s intelligible to hold that x is unconceived, then there is
some possible world w at which x exists and x is unconceived.
Principle of trans-world conceivability (PTC): If it’s true in w that x is unconceived, then there
is no thing y in any possible world such that y conceives of x as it is at w.
D. The modal argument
Hylas conceives that there is some x that is unconceived.
There is some x such that Hylas conceives of x as being unconceived. (1, PS)
If there is some x such that someone conceives of x as being unconceived, then there is
some possible world w at which x exists and x is unconceived. (PP)
There is some possible world w at which x exists and x is unconceived. (2,3)
If it’s true in w that x is unconceived, then there is no thing y in any possible world such
that y conceives of x as it is at w. (PTC)
There is no thing y in any possible world such that y conceives of x as it is at w. (4,5)
Hylas is in some possible world.
Hylas does not conceive of x. (6,7)
So Hylas both conceives of x and does not conceive of x (2,8).
Hylas is not (really) thinking that there are unconceived things. (1-9 reductio ad absurdum)
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