Review Materials for Chapter 7 – The Problem of Skepticism and Knowledge
Section 7.1 - Things Aren't Always What They Seem: Skepticism About Skepticism
1. Types of Knowledge.
Knowledge by acquaintance (knowing what)—experiential knowledge.
Performative knowledge (knowing how)—skill knowledge.
Propositional knowledge (knowing that)—factual knowledge.
2. Rationalism is the doctrine that reason is the only source of knowledge of the external world.
Empiricism is the doctrine that sense experience is the only source of knowledge of the external world.
3. An a-priori proposition is one that can be known prior to or independently of sense experience.
An a-posteriori proposition is one that can only be known after one has acquired sense experience.
4. An analytic proposition is a logical truth or one that can be turned into a logical truth by substituting
synonyms for synonyms.
A synthetic proposition is a proposition that is not analytic.
5. Theories of Truth.
According to the correspondence theory, a proposition is made true by its correspondence to reality.
According to the coherence theory, a proposition is made true by its coherence with a system of beliefs.
According to the pragmatic theory, a proposition is made true by its practical consequences.
6. According to cognitive subjectivism, a proposition is made true by ones believing it to be true.
According to cognitive cultural relativism, a proposition is made true by a society believing it to be true.
Objection: Both views are self-contradictory because a proposition and its negation could be believed to be
true.
7. Minimal Correspondence Theory of Truth.
The doctrine that a proposition is true if and only if things are as it says they are.
This preserves the insight that true propositions accurately represent reality without falling prey to the
criticisms that were fatal to the other theories of truth.
8. Greek Rationalism.
Heraclitus maintained that identity over time is an illusion. He thought that the world was being created
anew each instant.
“You cannot step into the same river twice,” he proclaimed, “for the water into which you first stepped has
flowed on.”
9. Parmenides thought that reality must contain a continuing substance, because only that which is
unchanging is real.
He reasoned that nonexistence (nothingness) cannot exist.
Therefore, everything that exists must always have existed.
From nothing, nothing comes, and nothing cannot come from something.
10. Plato, following Parmenides, held that only that which is unchanging is real, and, following Heraclitus, that
what is presented to our sense is constantly changing.
He concluded that what we sense isn’t fully real.
The prisoners in the cave see only the shadows cast by the truly real objects: the “forms.”
11. Descartes doubted that sense experience can give us knowledge because knowledge requires certainty and
nothing we learn through our senses is certain.
Descartes holds that you are justified in believing something to be true only if you are certain of it.
12. Descartes’s Dream thought experiment.
How often has it happened that you thought something was real only to find out that you were dreaming?
Can you know for certain that you’re not dreaming right now?
13. Descartes’s Dream Argument.
We can’t be certain that we’re not dreaming.
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If we can’t be certain that we’re not dreaming, we can’t be certain that what we sense is real.
If we can’t be certain that what we sense is real, we can’t acquire knowledge through sense experience.
Therefore, we can’t acquire knowledge through sense experience.
Descartes’s Evil Genius thought experiment.
Suppose that an evil genius used telepathy (or a mad scientist used electrodes) to put false ideas into your
mind.
Can you be certain that you’re not under the influence of such a person right now?
If not, can you have knowledge of the external world?
Descartes’s Evil Genius Argument.
We can’t be certain that our sense experience is not caused by an evil genius.
If we can’t be certain that our sense experience is not caused by an evil genius, we can’t be certain that what
we sense is real.
If we can’t be certain that what we sense is real, we can’t acquire knowledge through sense experience.
Therefore, we can’t acquire knowledge through sense experience.
Descartes cannot doubt that he is thinking, for doubting is a type of thinking.
And Descartes can’t doubt anything unless he exists.
So Descartes claims that he can be absolutely certain of one thing, namely, “I think, therefore I am.”
Descartes knows the contents of his mind; if he seems to see a tree, he knows that he seems to see a tree.
To acquire knowledge of the external world, he needs a principle to bridge the gap between appearance and
reality.
The Principle of Clarity and Distinctness.
God exists and is no deceiver.
If God exists and is no deceiver, then whatever I clearly and distinctly perceive is true.
Therefore, whatever I clearly and distinctly perceive is true.
Application of the Principle.
I clearly and distinctly seem to see a tree in front of me.
Whatever I clearly and distinctly perceive is true.
Therefore, there is a tree in front of me.
Cartesian Circle.
Descartes can’t know that God exists and is no deceiver unless he knows that what he clearly and distinctly
perceives is true.
But he can’t know that what he clearly and distinctly perceives is true unless he knows that God exists and is
no deceiver.
Foundationalism maintains that there are basic beliefs, that is, beliefs whose justification does not depend
on other beliefs.
Also, it maintains that the justification of all other beliefs depends, at least in part, on the basic beliefs
The problem of the Cartesian circle faces anyone who takes a foundationalist approach to knowledge.
The fact that we ordinarily claim to know many things that aren’t certain casts doubt on the claim that
knowledge requires certainty.
But if it’s doubtful that knowledge requires certainty, then Descartes can’t know that knowledge requires
certainty.
To know a proposition, it doesn’t have to be established beyond a shadow of a doubt. It only has to be
established beyond a reasonable doubt.
This is the standard that is used in courts of law to adjudicate matters of life and death; it can also be used to
adjudicate matters of knowledge and ignorance.
Empiricism leads to skepticism about anything that cannot be sensed.
Empiricists such as David Hume believe that only terms that stand for ideas derived from sense experience
can refer to real objects.
Empiricism leads to skepticism about anything that cannot be sensed.
Empiricists such as David Hume believe that only terms that stand for ideas derived from sense experience
can refer to real objects.
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The Kantian Synthesis.
Kant noticed that some truths can be known without being empirically confirmed, but also are not true by
definition.
26. According to Kant, to make sense of the world around us, we naturally categorize the world into a
conceptual scheme.
Section 7.2 – Facing Reality: Perception and the External World
1. Direct Realism is the doctrine that perception puts us in direct contact with reality.
“Direct” because nothing comes between the world and our perception of it.
“Realism” because there is an external world that is not affected by our thoughts.
2. The Argument from Illlusion.
What we see is bent.
The pencil is not bent.
So what we see is not the pencil.
3. Sense data are the objects that are immediately known in sensation, such as colors, sounds, smells,
hardnesses, roughnesses, etc.
4. The Problem of the External World.
We can’t compare our sense data with the world; all we can do is get more sense data.
So how can we know what the world is like in itself?
5. Representative realism is the doctrine that sensations are caused by external objects and that our sensations
represent those objects.
6. A primary quality is one possessed by material objects such as: solidity, extension, figure, and mobility.
A secondary quality is one that exists in the mind but not in material objects themselves such as: heat, color,
taste, etc.
According to Locke, sense data of primary qualities resemble the qualities of material objects.
7. Berkeley’s Objection.
Primary qualities such as figure and extension are as variable as secondary qualities.
What looks round from one angle can look elliptical from another.
Consequently, they can’t be considered to resemble qualities of physical objects.
8. Material objects are supposed to exist even when no one is thinking about (conceiving of) them.
Berkeley claims that material objects cannot exist because it’s impossible to conceive of something that exists
unconceived. (Once you conceive of it, it’s no longer unconceived!)
Since one cannot conceive of something existing unconceived, Berkeley concludes that it’s impossible for
something to exist unconceived.
Thus, everything that exists must be conceived by someone.
9. If to be is to be perceived, it would seem that when we stop perceiving something it ceases to exist.
But although we may stop perceiving something, God never stops perceiving anything.
So God holds things in existence by thinking about them.
10. There once was a young man who said “God
Must think it exceedingly odd
If he finds that this tree
Continues to be
When there’s no one about in the quad”
11. Dear Sir: Your astonishment’s odd
I am always about in the quad
And that’s why the tree
Will continue to be
Since observe by
Yours faithfully,
God
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12. Phenomenalism.
Berkeley held that things are nothing but patterns of sensations.
According to phenomenalism, all talk of things is reducible to talk of sensations.
Objection: What we perceive depends on the state of our bodies, but the state of our bodies cannot be
reduced to sensations.
13. It is not possible to conceive of something that exists unconceived.
But it is possible to conceive that something exists unconceived.
Thus the notion of material objects is not self-contradictory.
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