Rationalism and Rationalism and EmpiricismEmpiricism

Two Kinds of TruthsTwo Kinds of Truths

Before discussing the philosophers, it will Before discussing the philosophers, it will be helpful to begin by explaining an be helpful to begin by explaining an important view about how statements (or important view about how statements (or truths) can be classified into two main truths) can be classified into two main types. This distinction is important types. This distinction is important because it can help us understand the because it can help us understand the difference between rationalists and difference between rationalists and empiricists.empiricists.

Two Kinds of TruthTwo Kinds of Truth

Traditionally, there are two kinds of Traditionally, there are two kinds of truthtruth (1) NECESSARY (also called truths of (1) NECESSARY (also called truths of

reason)reason) (2) EMPIRICAL (also called contingent (2) EMPIRICAL (also called contingent

truths or truths of fact)truths or truths of fact)

NECESSARY TRUTHSNECESSARY TRUTHS

A statement expressing a necessary truth A statement expressing a necessary truth cannot possibly be false. It is true in all cannot possibly be false. It is true in all possible worlds. Examples:possible worlds. Examples:

All triangles have three sides.All triangles have three sides. All bachelors are unmarried.All bachelors are unmarried. No one who believes that God exists is an No one who believes that God exists is an

atheist.atheist.

Necessary TruthsNecessary Truths

It is important to see that the truth of a It is important to see that the truth of a necessary truth does not depend on what necessary truth does not depend on what the facts of the world are like. They are the facts of the world are like. They are always true no matter what. always true no matter what.

Necessary Truths and theNecessary Truths and theA PrioriA Priori

A PrioriA Priori = prior to experience or = prior to experience or independent of any experience of facts or independent of any experience of facts or states of affairs in the world.states of affairs in the world.

Necessary truths are often said to be true Necessary truths are often said to be true a priori, a priori, true independent of any particular true independent of any particular facts.facts.

Necessary Truths andNecessary Truths andA Priori TruthsA Priori Truths

It is also said that the proof (or It is also said that the proof (or justification) of a necessary truth does not justification) of a necessary truth does not depend on any particular facts of the depend on any particular facts of the world.world.

Empirical (or Contingent) TruthsEmpirical (or Contingent) Truths

Empirical = having to do with experience Empirical = having to do with experience Contingent = depending on experience Contingent = depending on experience

A statement expressing an empirical truth A statement expressing an empirical truth is true in virtue of the facts. An empirical is true in virtue of the facts. An empirical statement is empirical because its truth statement is empirical because its truth value (whether it is true or false) depends value (whether it is true or false) depends on what the world is like. on what the world is like.

Empirical (or Contingent) TruthsEmpirical (or Contingent) Truths

Empirical Statement: Microorganisms live Empirical Statement: Microorganisms live on Mars. on Mars.

Empirical truth: Over 6 billion people live Empirical truth: Over 6 billion people live on Earth.on Earth.

Empirical falsehood: Germany won WWII.Empirical falsehood: Germany won WWII.

Empirical Truths andEmpirical Truths andA Posteriori TruthsA Posteriori Truths

A posteriori = with experience or A posteriori = with experience or depending on experience of the factsdepending on experience of the facts

Empirical truths are sometimes called a Empirical truths are sometimes called a posteriori truths because empirical truths posteriori truths because empirical truths depend on what the facts are like, and depend on what the facts are like, and facts are known through some kind of facts are known through some kind of sense experience.sense experience.

Necessary and Empirical TruthsNecessary and Empirical Truths

Necessary TruthsNecessary Truths AnalyticAnalytic A prioriA priori

Empirical (or contingent) TruthsEmpirical (or contingent) Truths SyntheticSynthetic A posterioriA posteriori

Rationalism and EmpiricismRationalism and Empiricism

Now we can begin explaining the Now we can begin explaining the rationalist and empiricist approaches to rationalist and empiricist approaches to knowledge. We will also mention knowledge. We will also mention skepticism, because it is a problem that skepticism, because it is a problem that the rationalists and empiricists have to the rationalists and empiricists have to deal with.deal with.

Epistemic JustificationEpistemic Justification What can we know and how much do we know? What can we know and how much do we know?

To help answer these questions, we need a To help answer these questions, we need a theory of theory of epistemic justificationepistemic justification. Knowledge is . Knowledge is justifiedjustified true belief. If we can determine when true belief. If we can determine when and how our beliefs are and how our beliefs are justifiedjustified, then we can , then we can determine the determine the scope and limits of our scope and limits of our knowledgeknowledge. In broad strokes, there are three . In broad strokes, there are three main theories about epistemic justification: main theories about epistemic justification:

(1) Skepticism(1) Skepticism (2) Empiricism(2) Empiricism (3) Rationalism(3) Rationalism

SkepticismSkepticism SkepticismSkepticism says that there is no adequate says that there is no adequate

justification for our beliefs, so we can never attain justification for our beliefs, so we can never attain knowledge. We can have true beliefs, but no knowledge. We can have true beliefs, but no knowledge. knowledge.

Global SkepticismGlobal Skepticism denies that there can be denies that there can be knowledge of any kind about any subject matter. knowledge of any kind about any subject matter. Not many people hold global skepticism, but it is Not many people hold global skepticism, but it is hard to defeat in conversation hard to defeat in conversation

Local SkepticismLocal Skepticism denies that we can have denies that we can have knowledge regarding some subject matters, but not knowledge regarding some subject matters, but not all, or that some methods of justification are not all, or that some methods of justification are not reliable (like reading fortune cookies, astrology, reliable (like reading fortune cookies, astrology, psychic hotlines, alternative medicine, or TV news).psychic hotlines, alternative medicine, or TV news).

EmpiricismEmpiricism

An empiricist holds that our beliefs can be best An empiricist holds that our beliefs can be best justified in light of the evidence we receive from justified in light of the evidence we receive from our senses. We therefore can know something if our senses. We therefore can know something if we can justify it with respect to what we see, we can justify it with respect to what we see, hear, and feel about the world. According to hear, and feel about the world. According to empiricism, natural sciences like physics, empiricism, natural sciences like physics, chemistry, and biology produce the most reliable chemistry, and biology produce the most reliable knowledge. We can know something if we can knowledge. We can know something if we can justify it through what we can experience justify it through what we can experience through our senses. through our senses.

EmpiricismEmpiricism

Criticism of rationalismCriticism of rationalism Necessary truths are just Necessary truths are just tautologiestautologies (true by (true by

definition or true analytically or true in virtue of definition or true analytically or true in virtue of logical form) and don’t say much about the logical form) and don’t say much about the world.world.

Rationalists produce absurd metaphysical Rationalists produce absurd metaphysical claims about reality because they go too far claims about reality because they go too far and end up making bogus and end up making bogus a prioria priori claims that claims that are also are also syntheticsynthetic in order to say something in order to say something meaningful about the world.meaningful about the world.

EmpiricistsEmpiricists John Locke (1632-1704)John Locke (1632-1704) Bishop Berkeley (1685-1753)Bishop Berkeley (1685-1753) David Hume (1711-1776)David Hume (1711-1776) John Stuart Mill (1806-1873)John Stuart Mill (1806-1873) Bertrand Russell (1872-1970)Bertrand Russell (1872-1970) Logical Positivists: A.J. Ayer (1910-1989)Logical Positivists: A.J. Ayer (1910-1989) William James (1842-1910)William James (1842-1910)

RationalismRationalism

A rationalist believes that our beliefs can A rationalist believes that our beliefs can be best justified in light of rational be best justified in light of rational evidence, not sensory evidence. We can evidence, not sensory evidence. We can know something if it appears true in the know something if it appears true in the light of reason, not our senses. According light of reason, not our senses. According to rationalism, mathematics and logic to rationalism, mathematics and logic provide the most reliable knowledge.provide the most reliable knowledge.

RationalistsRationalists

Plato could be called a rationalistPlato could be called a rationalist Rene Descartes (1556-1650)Rene Descartes (1556-1650) Baruch Spinoza (1632-1677)Baruch Spinoza (1632-1677) Gottfried Leibniz (1646-1716)Gottfried Leibniz (1646-1716)

EmpiricismEmpiricism

Empiricists believe that knowledge is Empiricists believe that knowledge is acquired through sense experience.acquired through sense experience.

So there has to be some theory of So there has to be some theory of perception that connects sense perception that connects sense experience with reality: experience with reality: Whenever I perceive that object S has Whenever I perceive that object S has

property P, S really has P.property P, S really has P.

Empiricism:Empiricism:3 Theories of Perception3 Theories of Perception

Naïve RealismNaïve Realism RepresentationalismRepresentationalism IdealismIdealism

Empiricism: Naïve RealismEmpiricism: Naïve Realism

Naïve Realism: What you see is what you Naïve Realism: What you see is what you get. When I perceive that object S has get. When I perceive that object S has property P, S really has property P. property P, S really has property P.

Objection to Naïve RealismObjection to Naïve Realism

It is not always the case that what I see is the It is not always the case that what I see is the truth. There is a difference between appearance truth. There is a difference between appearance and reality, and sometimes appearances are and reality, and sometimes appearances are deceiving.deceiving. Illusions and miragesIllusions and mirages People’s experiences differ: a wind may feel cold to People’s experiences differ: a wind may feel cold to

me but warm to you. Who is correct?me but warm to you. Who is correct? The buckets-of-water example: Rest one hand in The buckets-of-water example: Rest one hand in

freezing water and one in hot water. Take both hands freezing water and one in hot water. Take both hands out and put them into a bucket of warm water. The out and put them into a bucket of warm water. The water in the bucket will feel hot to the cold hand and water in the bucket will feel hot to the cold hand and cold to the hot hand. Which hand is giving the correct cold to the hot hand. Which hand is giving the correct feeling?feeling?

Empiricism: RepresentationalismEmpiricism: Representationalism

Representationalism: Our ideas (which Representationalism: Our ideas (which come from sense experience) are come from sense experience) are representations of the external world. representations of the external world. There is a difference between appearance There is a difference between appearance and reality, and we do not directly and reality, and we do not directly experience reality. We only directly experience reality. We only directly perceive our sense impressions. Some of perceive our sense impressions. Some of what we experience is in reality.what we experience is in reality.

John Locke: Theory of knowledge John Locke: Theory of knowledge and Representationalismand Representationalism

We are born with minds that are like blank We are born with minds that are like blank slates. There are no innate ideas. The view that slates. There are no innate ideas. The view that there are innate ideas is dangerous and can be there are innate ideas is dangerous and can be used to control people.used to control people.

There are two sources of ideas: (1) sensation There are two sources of ideas: (1) sensation (sense experience of sense objects) and (2) (sense experience of sense objects) and (2) reflectionreflection

The ideas of reflection are produced from the The ideas of reflection are produced from the mind’s working on the ideas of sensation: mind’s working on the ideas of sensation: perceiving, doubting, thinking, believing, perceiving, doubting, thinking, believing, reasoning, knowing, willing.reasoning, knowing, willing.

Locke: Knowledge and Locke: Knowledge and RepresentationalismRepresentationalism

There are two kinds of ideas: (1) simple There are two kinds of ideas: (1) simple and (2) complex.and (2) complex.

Simple ideas are those like the idea of the Simple ideas are those like the idea of the color yellow (from sensation) or the idea of color yellow (from sensation) or the idea of pain (from reflection) that cannot be pain (from reflection) that cannot be broken down into other ideas.broken down into other ideas.

Complex ideas are made up of simple Complex ideas are made up of simple ideas. The mind can put simple ideas ideas. The mind can put simple ideas together to make a complex idea, like the together to make a complex idea, like the idea of a golden mountain.idea of a golden mountain.

Locke: Knowledge and Locke: Knowledge and RepresentationalismRepresentationalism

The mind creates complex ideas. The The mind creates complex ideas. The mind:mind:

(1) joins ideas(1) joins ideas (2) brings them together to compare them(2) brings them together to compare them (3) abstracts (abstract the idea of “man” (3) abstracts (abstract the idea of “man”

from my experiences of John and Harry.)from my experiences of John and Harry.)

Representationalism: Primary and Representationalism: Primary and Secondary QualitiesSecondary Qualities

There are two kinds of qualities. A quality is the There are two kinds of qualities. A quality is the power in an object to produce any idea in my power in an object to produce any idea in my mind.mind.

Primary qualities are those that really do exist in Primary qualities are those that really do exist in the bodies themselves. These include: Shape, the bodies themselves. These include: Shape, Solidity, Extension, Motion or Rest, NumberSolidity, Extension, Motion or Rest, Number

Secondary qualities are those that do not really Secondary qualities are those that do not really exist in the bodies themselves. These include: exist in the bodies themselves. These include: Tastes, Colors, Sounds, Odors, and certain Tastes, Colors, Sounds, Odors, and certain Feelings of Touch, like softness or roughness.Feelings of Touch, like softness or roughness.

Locke: SubstanceLocke: Substance Qualities do not just float around. They Qualities do not just float around. They

have to be in something. Something has to have to be in something. Something has to hold them together and organize them. hold them together and organize them. The power to produce ideas in my mind The power to produce ideas in my mind has to be in something. This something is has to be in something. This something is substancesubstance, which Locke takes to be , which Locke takes to be matter. matter.

Substance is matter, but we cannot say Substance is matter, but we cannot say what it is because we never perceive it. what it is because we never perceive it.

A Problem with A Problem with RepresentationalismRepresentationalism

How can we ever know if our ideas really How can we ever know if our ideas really represent an external reality? If all I ever represent an external reality? If all I ever directly perceive (in my mind) are the directly perceive (in my mind) are the ideas, and not the external objects ideas, and not the external objects themselves, then how can I ever know for themselves, then how can I ever know for sure what that external reality is like at all? sure what that external reality is like at all? How can I ever know that an external How can I ever know that an external reality exists at all?reality exists at all?

Berkeley: IdealismBerkeley: Idealism Berkeley argues that if we are true Berkeley argues that if we are true

empiricists, then we have to reject Locke’s empiricists, then we have to reject Locke’s idea of substance, or matter, because it is idea of substance, or matter, because it is never perceived. Matter is a meaningless never perceived. Matter is a meaningless term.term.

Berkeley argues that there is no mind- Berkeley argues that there is no mind- independent substance. The existence of independent substance. The existence of anything depends on a perceiving mind.anything depends on a perceiving mind.

““Esse Est PercipiEsse Est Percipi” – To be is to be ” – To be is to be perceived (by a mind).perceived (by a mind).

Berkeley: IdealismBerkeley: Idealism Rejects Locke’s distinction between primary and Rejects Locke’s distinction between primary and

secondary qualities. There are no mind-secondary qualities. There are no mind-independent qualities, no-primary qualities. independent qualities, no-primary qualities. Every quality is like a secondary quality. Every Every quality is like a secondary quality. Every quality is experienced through a perceiving quality is experienced through a perceiving mind. Only sensed qualities are real.mind. Only sensed qualities are real.

““In truth, the object and the sensation are the In truth, the object and the sensation are the same thing, and cannot therefore be abstracted same thing, and cannot therefore be abstracted from each other.”from each other.”

Locke had removed beauty (and other Locke had removed beauty (and other secondary qualities) from the world. This made secondary qualities) from the world. This made the world ugly.the world ugly.

Berkeley: IdealismBerkeley: Idealism If the object is the same thing as the If the object is the same thing as the

sensation, then this beings up the problem sensation, then this beings up the problem that we that we return to a kind of naïve realismreturn to a kind of naïve realism. . What we see is what we get. There seems What we see is what we get. There seems to be no basis for the distinction between to be no basis for the distinction between appearance and reality. Our ideas do not appearance and reality. Our ideas do not represent an external mind-independent represent an external mind-independent world that we can be mistaken about.world that we can be mistaken about.

Berkeley: IdealismBerkeley: Idealism

Another problem is that it seems that for Another problem is that it seems that for anything to exist, it has to be perceived by anything to exist, it has to be perceived by a mind. But if a tree falls in the woods and a mind. But if a tree falls in the woods and no one is there to hear it, does it make a no one is there to hear it, does it make a sound?sound?

If we all close our eyes, does the world If we all close our eyes, does the world disappear?disappear?

Berkeley: IdealismBerkeley: Idealism

So What is the cause of our ideas if not So What is the cause of our ideas if not the power in some mind-independent the power in some mind-independent material substance to produce ideas in our material substance to produce ideas in our minds? What keeps our ideas together?minds? What keeps our ideas together?

Berkeley: IdealismBerkeley: Idealism God is the source of our ideas. God is the God is the source of our ideas. God is the

mind that perceives all things. God is the mind that perceives all things. God is the (spiritual) substance behind all things.(spiritual) substance behind all things.

God sees the tree fall, so it does make a God sees the tree fall, so it does make a sound.sound.

Berkeley finds room for non-physical Berkeley finds room for non-physical spiritual beings and rejects Locke’s spiritual beings and rejects Locke’s materialism which seems to lead to materialism which seems to lead to atheism.atheism.

Berkeley’s InstrumentalismBerkeley’s Instrumentalism The abstract ideas of scientists, like the ideas of The abstract ideas of scientists, like the ideas of

force, attraction, and gravity, do not refer to force, attraction, and gravity, do not refer to anything real. Only sensed qualities exist. There anything real. Only sensed qualities exist. There is nothing other than what we can perceive. But is nothing other than what we can perceive. But these ideas are still useful ideas that can help us these ideas are still useful ideas that can help us explain things. They just do not refer to anything explain things. They just do not refer to anything real.real.

There is no causality. We never see that. Things There is no causality. We never see that. Things just follow each other in time: A follows B, but it just follow each other in time: A follows B, but it is never possible to say that A is the cause of B.is never possible to say that A is the cause of B.

God orders the behavior of all things.God orders the behavior of all things.

Hume: EmpiricismHume: Empiricism

Explaining a similar empiricist view, Hume Explaining a similar empiricist view, Hume distinguished between (1) impressions and distinguished between (1) impressions and (2) ideas(2) ideas

Every idea comes from some impression Every idea comes from some impression from sense experience.from sense experience.

Hume: EmpiricismHume: Empiricism

If a term has any meaning, then it must be If a term has any meaning, then it must be connected to an idea derived from some connected to an idea derived from some sense impression. If it is not, then the term sense impression. If it is not, then the term is meaningless.is meaningless.

Hume: Empiricism and SkepticismHume: Empiricism and Skepticism Hume thinks that if we are strict empiricists, then Hume thinks that if we are strict empiricists, then

it is going to be very hard or impossible to it is going to be very hard or impossible to answer these questions:answer these questions:

Is there an Is there an external worldexternal world?? Can Can inductioninduction really work? really work? Can we ever know the ultimate Can we ever know the ultimate substancesubstance?? Is there a Is there a selfself?? Is there Is there causalitycausality (as necessary connection)? (as necessary connection)? Is there a Is there a GodGod??