Chapter 7The Problem of Skepticism

and Knowledge

McGraw-Hill © 2013 McGraw-Hill Companies. All Rights Reserved.

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The Problem of Knowledge and Skepticism

How is knowledge of the external world possible given that our only source of knowledge is sense experience?

What is it to have knowledge? Must you be justified in believing

something in order to know it?

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Types of Knowledge

Knowledge by acquaintance (knowing what)—experiential knowledge.

Performative knowledge (knowing how)—skill knowledge.

Propositional knowledge (knowing that)—factual knowledge.

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Rationalism vs. Empiricism

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.

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A-priori vs. A-posteriori Propositions

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.

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Analytic vs. Synthetic Propositions

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.

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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.

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Cognitive Subjectivism and Cultural Relativism According to cognitive subjectivism, a

proposition is made true by an individual’s 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 both be believed to be true.

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Minimal Correspondence Theory

The doctrine that a proposition is true if and only if things are as it says they are.

Advantages: Preserves the insight that propositions are

made true by the way the world is. Doesn’t fall prey to the criticisms that were

fatal to the other theories of truth.

Section 7.1Things Aren’t AlwaysWhat They Seem

Skepticism about Skepticism

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Heraclitus

Everything is in flux--the world is being created anew each instant.

“You cannot step into the same river twice, for the water into which you first stepped has flowed on.”

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Parmenides

Only that which is unchanging is real.

Nonexistence (nothingness) cannot exist.

From nothing, nothing comes. So reality must be composed of

an eternal, unchanging substance.

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Thought Probe: Thinking about Nothing

Paramenides believed that because nonexistence cannot exist, it cannot be thought about.

Do you agree? Can you think about nothing? That is, can nothingness be the object of your thought?

If so, can you describe what you’re thinking about when you’re thinking about nothing?

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Thought Probe:Zeno’s Paradox of Bisection

To exit the stadium, you must reach the halfway point. But before you get there, you must reach a point halfway to that.

Since there are an infinite number of halfway points, it would take you an infinite time to pass through them all and get out.

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Plato’s Allegory of the Cave

Plato agreed with Parmenides that only that which is unchanging is real and with Heraclitus, that what we 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.”

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Thought Probe:Innate Knowledge

Do you think that there are any concepts or truths that all normal humans have or know?

If so, what are they?

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Cartesian Skepticism

Sense experience can’t give us knowledge because knowledge requires certainty and nothing we learn through our senses is certain.

We can know something only if we are certain that it is true.

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Thought Experiment: Descartes’s Dream

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?

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Thought Probe: Dreams and Reality

Suppose that every dream you had ended by your getting into bed and going to sleep.

Would you be able to tell what was a dream and what was reality? How?

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Descartes’s Dream Argument

1. We can’t be certain that we’re not dreaming.

2. If we can’t be certain that we’re not dreaming, we can’t be certain that what we sense is real.

3. If we can’t be certain that what we sense is real, we can’t acquire knowledge through sense experience.

4. Therefore, we can’t acquire knowledge through sense experience.

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Thought Experiment: Descartes’s Evil Genius (Unger’s Mad Scientist)

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?

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The Evil Genius Argument

1. We can’t be certain that our sense experience is not caused by an evil genius.

2. 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.

3. If we can’t be certain that what we sense is real, we can’t acquire knowledge through sense experience.

4. Therefore, we can’t acquire knowledge through sense experience.

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Cartesian Certainty

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.”

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What Descartes Knows

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.

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The Principle of Clarity and Distinctness

1. God exists and is no deceiver.

2. If God exists and is no deceiver, then whatever I clearly and distinctly perceive is true.

3. Therefore, whatever I clearly and distinctly perceive is true.

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Application of the Principle of Clarity and Distinctness

1. I clearly and distinctly seem to see a tree in front of me.

2. Whatever I clearly and distinctly perceive is true.

3. Therefore, there is a tree in front of me.

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The 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.

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Foundationalism

The doctrine that there are basic beliefs, that is, beliefs whose justification does not depend on other beliefs.

The justification of all other beliefs depends, at least in part, on the basic beliefs.

Problem: How are those beliefs justified?

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Reasonable Doubt

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.

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Shadow of a Doubt vs. Reasonable Doubt

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 used by courts to adjudicate matters of life and death; it can also be used to adjudicate matters of knowledge and ignorance.

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Empiricism

The doctrine that our only source of knowledge about the external world is sense experience.

If something cannot be sensed, it cannot be known.

So the existence of God, the soul, or the afterlife cannot be known.

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The Problem of Induction

Induction assumes that the future will resemble the past.

That belief can’t be justified a-posteriori because all a-posteriori reasoning assumes its truth.

That belief can’t be justified a-priori because its falsity doesn’t imply a contradiction.

So it looks like that belief can’t be justified.

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Thought Probe: Science and Faith

We can’t prove that the future will resemble the past (that like causes produce like effects).

Yet all scientific inferences are based on that belief.

Is science, then, based on faith? Is science a form of religion?

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The Kantian Synthesis

Kant agrees with Hume that the claim that like causes will produce like effects is synthetic because it’s not true by definition.

Yet he believes that it can be known a-priori because it makes objective experience (experience of objects) possible.

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The Kantian Synthesis

According to Kant, the mind is an information processor.

It takes raw sense experience and brings it under certain concepts (like causality).

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Thought Probe: Constructing Reality Are scientific laws invented or discovered? The traditional view: scientific laws exist “out

there” in the world and science discovers them. Kant’s view: “The order and regularity of the

appearance we entitle nature, we ourselves introduce.”

For Kant, reality is a human construct. Which view do you think is correct? Why?

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Mystical Experience

Some have sought to transcend our conceptual scheme and have a direct experience of reality.

Mystics believe that only through such direct experience can we acquire an understanding of the true nature of reality.

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Mystical Experience

Because mystical experience has not been conceptualized, it cannot be described—it is “ineffable.”

But ineffable experiences can’t be compared.

So we have no way to tell true mystical experiences from false ones.

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Mystical Experience

Many Eastern mystical traditions try to achieve mystical enlightenment by emptying ones’ mind of all thoughts.

But an empty mind may not be directed on anything.

In that case, it can’t tell us anything about reality.

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Mystical Experience

An experience’s being mystical doesn’t guarantee either its truth or falsity.

But the only way to tell whether it’s true, is to put it to the test.

Only that which can withstand such critical scrutiny deserves to be called “true.”