Knowledge, Knowledge, Skepticism, Skepticism,

and Descartesand Descartes

KnowingKnowing

In normal life, we distinguish between In normal life, we distinguish between knowingknowing and just and just believingbelieving. . ““I think the keys are in my pocket.”I think the keys are in my pocket.” ““I I knowknow the keys are in my pocket.” the keys are in my pocket.” ““I believe 0.999999999… = 1.”I believe 0.999999999… = 1.” ““I I knowknow 0.999999999… = 1.” 0.999999999… = 1.”

The traditional definition of The traditional definition of knowledgeknowledge

In cases where we In cases where we knowknow a claim, we have good a claim, we have good reason to think it is true: we feel the keys in our reason to think it is true: we feel the keys in our hands, or we do the math, etc.hands, or we do the math, etc.

Knowledge is Knowledge is justified true beliefjustified true belief. (This definition . (This definition goes back to Plato.) To goes back to Plato.) To knowknow a claim, you must a claim, you must believe it, it must be true, and you must have believe it, it must be true, and you must have good reason to believe it is true.good reason to believe it is true.

A skeptic is someone who argues that we A skeptic is someone who argues that we can’t can’t justifyjustify certain types of claims. certain types of claims.

SkepticismSkepticism

SkepticismSkepticism = the view that we = the view that we cannotcannot knowknow that that claims of some type are true (= we’re claims of some type are true (= we’re notnot ableable to to have good reasons to believe they are true).have good reasons to believe they are true). So a So a religious skeptic religious skeptic thinks we can’t know religious thinks we can’t know religious

claims, a claims, a moral skepticmoral skeptic thinks we can’t know moral thinks we can’t know moral claims, etc.claims, etc.

We will examine two kinds of skepticism that interest We will examine two kinds of skepticism that interest philosophers: skepticism about the philosophers: skepticism about the external worldexternal world and and skepticism about skepticism about inductioninduction (reasoning about the (reasoning about the unobservedunobserved).).

How could you be skeptical of the How could you be skeptical of the external world?external world?

Normally, we think we know lots of things. Normally, we think we know lots of things. I know I am wearing shoes right now, I I know I am wearing shoes right now, I know that Sacramento is the capital of know that Sacramento is the capital of California, and so on. It would seem crazy California, and so on. It would seem crazy to say “I don’t know, I only believe” for any to say “I don’t know, I only believe” for any of these beliefs.of these beliefs.

But there are arguments that we But there are arguments that we can’tcan’t know such claims.know such claims.

Rene Descartes (1596-1650)Rene Descartes (1596-1650)

Descartes was (in our terms) a Descartes was (in our terms) a scientist and mathematician. scientist and mathematician.

He invented analytic geometry, He invented analytic geometry, demonstrating that geometry can demonstrating that geometry can be reduced to algebra.be reduced to algebra.

Compare the ancient way of doing Compare the ancient way of doing geometry with Descartes’:geometry with Descartes’:

Euclid’s definition of a circleEuclid’s definition of a circle

‘‘A plane figure contained by one line such A plane figure contained by one line such that all straight lines falling upon it from that all straight lines falling upon it from one point amongst those lying within the one point amongst those lying within the circle (called the center) are equal to one circle (called the center) are equal to one another.’another.’

Descartes’ definition of a circleDescartes’ definition of a circle

‘‘A circle is all A circle is all xx and and yy satisfying satisfying x² + y² = r² x² + y² = r² for some constant number for some constant number r.r.’’

Descartes’ mathematical and Descartes’ mathematical and scientific achievementsscientific achievements

Using analytic geometry, problems such as Using analytic geometry, problems such as finding the distance between any two points finding the distance between any two points becomes simple algebra.becomes simple algebra.

He introduced the use of He introduced the use of x, y,x, y, and and zz as as variables, and variables, and a, b,a, b, and and cc as constants, as well as constants, as well as the standard notations for cubes and roots.as the standard notations for cubes and roots.

He used trigonometry to find the sine-law of the He used trigonometry to find the sine-law of the refraction of light (Snell’s law).refraction of light (Snell’s law).

And he applied this to explain rainbows.And he applied this to explain rainbows.

Descartes vs. skepticismDescartes vs. skepticism

Descartes lived in a time of intellectual Descartes lived in a time of intellectual turmoil and uncertainty (the Reformation turmoil and uncertainty (the Reformation and the beginning of the Scientific and the beginning of the Scientific Revolution).Revolution).

He rejected trust in authority and the He rejected trust in authority and the senses: they were often wrong.senses: they were often wrong.

But he also wanted to disprove skeptics, to But he also wanted to disprove skeptics, to provide a foundation for science.provide a foundation for science.

Descartes’ Descartes’ Meditations Meditations (1640)(1640)

At the start of the First Meditation, At the start of the First Meditation, Descartes points out that, over the course Descartes points out that, over the course of our lives, we have many false beliefs. of our lives, we have many false beliefs.

Descartes wants to find an absolutely Descartes wants to find an absolutely certain start for knowledge: beliefs he can certain start for knowledge: beliefs he can use as the foundations of science.use as the foundations of science.

These beliefs must be absolutely certain: These beliefs must be absolutely certain: they must be immune to any doubt.they must be immune to any doubt.

Cartesian DoubtCartesian Doubt

So Descartes uses doubt, but only to find So Descartes uses doubt, but only to find absolute certainty. absolute certainty.

Whatever beliefs can withstand the most Whatever beliefs can withstand the most extreme doubt are absolutely certain.extreme doubt are absolutely certain.

Descartes imagines three extreme forms Descartes imagines three extreme forms of doubt:of doubt:

1.1. My senses are unreliableMy senses are unreliable2.2. I could be dreamingI could be dreaming3.3. I could be controlled by a godlike demonI could be controlled by a godlike demon

Descartes’ illusion argumentDescartes’ illusion argument

1.1. My senses sometimes deceive me in My senses sometimes deceive me in ways that I can’t tell the difference ways that I can’t tell the difference between true and false.between true and false.

2.2. If (1), then any belief based on the If (1), then any belief based on the senses could be false.senses could be false.

3.3. So, I don’t So, I don’t knowknow beliefs based on the beliefs based on the senses.senses.

Descartes’ dream argumentDescartes’ dream argument

1.1. There is no criterion by which I can be There is no criterion by which I can be sure that I am not dreaming.sure that I am not dreaming.

2.2. If (1), then every belief based on If (1), then every belief based on experience could easily be false.experience could easily be false.

3.3. So, every belief based on experience is So, every belief based on experience is not knowledge.not knowledge.

Descartes’ demon argumentDescartes’ demon argument

1.1. I cannot prove that I cannot prove that there is no demon.there is no demon.

2.2. If (1), then all of my If (1), then all of my beliefs could easily beliefs could easily be false.be false.

3.3. So, no beliefs are So, no beliefs are knowledge.knowledge.

The brain in a vatThe brain in a vat

Skepticism about the external worldSkepticism about the external world

Recap: to know something, we need good Recap: to know something, we need good reason to believe it is true.reason to believe it is true.

If I were a BIV, all my reasons for believing If I were a BIV, all my reasons for believing an external world exists would be the an external world exists would be the same, but those beliefs would be same, but those beliefs would be falsefalse..

So: those reasons So: those reasons are not goodare not good reasonsreasons.. So: So: we do we do notnot have good reason to believe have good reason to believe

there is an external worldthere is an external world..

What the skeptic What the skeptic isn’tisn’t claiming claiming

Skeptics Skeptics don’tdon’t claim to claim to knowknow we are brains in a we are brains in a vat. vat. They are saying They are saying no one knows one way or no one knows one way or the otherthe other: : we have no good reasons to show that we have no good reasons to show that we are or are not envatted.we are or are not envatted.

Skeptics Skeptics aren’taren’t just saying we can’t be just saying we can’t be certaincertain the the world is real. world is real. They are saying They are saying moremore than that: than that: they are saying you have they are saying you have no good reason no good reason to to believe the external world over the virtual world in believe the external world over the virtual world in a vata vat..

Skeptics Skeptics aren’taren’t saying we know nothing. saying we know nothing. (That (That would be would be knowledgeknowledge!) !) They are saying we They are saying we don’t don’t knowknow there is an external world there is an external world..

Descartes’ solutionDescartes’ solution

So, after the First Meditation, Descartes’ So, after the First Meditation, Descartes’ goal is clear: he must defeat the demon goal is clear: he must defeat the demon hypothesis. That is, he needs to prove hypothesis. That is, he needs to prove that there is no demon. If he can’t, then that there is no demon. If he can’t, then he doesn’t have knowledge of the world.he doesn’t have knowledge of the world.

The flip side, though, is optimistic: if he The flip side, though, is optimistic: if he can defeat the demon, then he has a can defeat the demon, then he has a foundation for knowledge immune to the foundation for knowledge immune to the most extreme skepticism.most extreme skepticism.

Descartes’ solution: Descartes’ solution: Cogito ergo sumCogito ergo sum

1.1. I am thinking.I am thinking.

2.2. Whatever thinks, exists.Whatever thinks, exists.

3.3. Therefore, I exist.Therefore, I exist.

or:or:

1.1. I could be dreaming or be deceived by a demon.I could be dreaming or be deceived by a demon.

2.2. But even if I am dreaming, or some demon is But even if I am dreaming, or some demon is deceiving me, then I exist.deceiving me, then I exist.

3.3. Therefore, I exist.Therefore, I exist.

Descartes’ way back to knowledgeDescartes’ way back to knowledge

Given that “I exist” is absolutely certain, how Given that “I exist” is absolutely certain, how can we get to the sort of scientific can we get to the sort of scientific knowledge that Descartes wants to knowledge that Descartes wants to justify?justify?

Descartes proposes two reinforcing ways:Descartes proposes two reinforcing ways:1.1. Prove God exists.Prove God exists.

2.2. Take clear and distinct ideas as the Take clear and distinct ideas as the standard of certain knowledge.standard of certain knowledge.

Descartes’ proof of GodDescartes’ proof of God

1.1. We have an idea of God as an infinite, real We have an idea of God as an infinite, real being.being.

2.2. The cause of any idea must have at least The cause of any idea must have at least as much reality as the idea has.as much reality as the idea has.

3.3. So, there is something with infinite, real So, there is something with infinite, real being.being.

4.4. If there is something with infinite, real If there is something with infinite, real being, then it is God.being, then it is God.

5.5. So, God exists.So, God exists.

God and knowledgeGod and knowledge

If God exists and is If God exists and is perfect, then God perfect, then God wouldn’t allow us to wouldn’t allow us to be deceived by a be deceived by a demon.demon.

So Descartes thinks So Descartes thinks he has disproved the he has disproved the demon hypothesis.demon hypothesis.

Clear and distinct ideasClear and distinct ideas

Also, Descartes claims that Also, Descartes claims that clear and distinct ideas clear and distinct ideas (“present and accessible to the attentive mind … (“present and accessible to the attentive mind … sharply separated from all others so it contains sharply separated from all others so it contains only what is clear”) are “certain and indubitable.”only what is clear”) are “certain and indubitable.”

Knowing that ‘I exist’ is such an idea.Knowing that ‘I exist’ is such an idea. Other judgments that meet that standard are true. Other judgments that meet that standard are true.

Mathematical truths (2+2=3+1; a triangle has three Mathematical truths (2+2=3+1; a triangle has three sides) are good examples.sides) are good examples.

So reason gives us genuine knowledge. This is So reason gives us genuine knowledge. This is what makes Descartes a what makes Descartes a rationalistrationalist..

Descartes: SummaryDescartes: Summary

Descartes’ anti-skeptical, rationalist theory Descartes’ anti-skeptical, rationalist theory of knowledge:of knowledge: ““Cogito ergo sum” provides a first example of Cogito ergo sum” provides a first example of

something known, and reveals what is something known, and reveals what is needed: needed: clear and distinct ideasclear and distinct ideas..

Then we prove clearly and distinctly that the Then we prove clearly and distinctly that the idea of God implies a perfect cause, i.e., God.idea of God implies a perfect cause, i.e., God.

A perfect God cannot deceive, so our senses A perfect God cannot deceive, so our senses and reason are reliable and reason are reliable if used properly if used properly (if (if guided by clear & distinct ideas, e.g., math).guided by clear & distinct ideas, e.g., math).

Arnauld’s criticismArnauld’s criticism

““I have an uncertainty as to I have an uncertainty as to how circular reasoning is how circular reasoning is to be avoided in saying the to be avoided in saying the only secure reason we only secure reason we have for believing what is have for believing what is clear and distinct is that clear and distinct is that God exists … and we can God exists … and we can be sure that God exists be sure that God exists only because we clearly only because we clearly and distinctly perceive and distinctly perceive that.”that.”

Parting thoughts on DescartesParting thoughts on Descartes

Descartes thought he had defeated Descartes thought he had defeated skepticism and laid a rationalist foundation skepticism and laid a rationalist foundation for knowledge (mathematical science).for knowledge (mathematical science).

But his extreme version of skepticism was But his extreme version of skepticism was not as easy to defeat as he thought.not as easy to defeat as he thought.

Reason was key to science, but it still Reason was key to science, but it still wasn’t clear how we could prove that we wasn’t clear how we could prove that we have knowledge.have knowledge.

The regress of justificationThe regress of justification Suppose that I believe Suppose that I believe PP, and , and P P is to be justified. is to be justified.

Its justification will be other beliefs. But then if Its justification will be other beliefs. But then if PP is is to be justified, these other beliefs must be justified to be justified, these other beliefs must be justified too, and so on…too, and so on…

How to prevent an infinite regress? Perhaps some How to prevent an infinite regress? Perhaps some beliefs are justified in a way that does not depend beliefs are justified in a way that does not depend on any other belief. Descartes took this route: on any other belief. Descartes took this route: foundationalismfoundationalism, taking some beliefs to be self-, taking some beliefs to be self-evident or self-justifying. evident or self-justifying.

Avoiding skepticism by Avoiding skepticism by redefining knowledgeredefining knowledge

But perhaps the problem was assuming But perhaps the problem was assuming that that to knowto know = = to have justified true belief.to have justified true belief.

The JTB definition has serious problems: if The JTB definition has serious problems: if knowledge must be justified, then an knowledge must be justified, then an infinite regress implies there is no infinite regress implies there is no knowledge. And Gettier counter-examples knowledge. And Gettier counter-examples show JTB is too broad.show JTB is too broad.

So what’s important in “knowing”?So what’s important in “knowing”?

The Causal Theory of The Causal Theory of KnowledgeKnowledge

An An internalistinternalist claims knowledge must be claims knowledge must be justifiable in reasons that the believer is justifiable in reasons that the believer is able to be conscious of.able to be conscious of.

An An externalistexternalist claims that knowledge claims that knowledge depends on having a reliable causal depends on having a reliable causal connection to whatever makes a belief connection to whatever makes a belief true, even if that connection is unknown to true, even if that connection is unknown to the believer (“outside the believer’s mind”).the believer (“outside the believer’s mind”).

Externalism Externalism (The Causal Theory of Knowledge)(The Causal Theory of Knowledge)

Externalists replace justification (giving Externalists replace justification (giving reasons) with reasons) with reliablereliable causationcausation (what happens (what happens to make you believe it).to make you believe it).

A “reliable cause” would be one that almost A “reliable cause” would be one that almost always causes true beliefs.always causes true beliefs.

The believer doesn’t have to understand how The believer doesn’t have to understand how knowing causes true beliefs. Example: you knowing causes true beliefs. Example: you may recognize a musical key without being may recognize a musical key without being able to explain it.able to explain it.

A challenge for the externalistA challenge for the externalist

While externalism promisingly solves regress While externalism promisingly solves regress and Gettier problems, it raises a puzzle of its and Gettier problems, it raises a puzzle of its own: what if a person doubts their own reliably own: what if a person doubts their own reliably caused beliefs?caused beliefs?

Suppose a doctor has a real causal ability to Suppose a doctor has a real causal ability to recognize illness. But she dismisses it recognize illness. But she dismisses it because she doesn’t want to risk a patient’s because she doesn’t want to risk a patient’s life on her hunch. Isn’t knowing supposed to life on her hunch. Isn’t knowing supposed to guide action?guide action?