1. Rationalism and Empiricism

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

3. Two Kinds of Truth Traditionally, there are two kinds of truth
(1) NECESSARY (also called truths of reason)
(2) EMPIRICAL (also called contingent truths or truths of fact)

4. NECESSARY TRUTHS
A statement expressing a necessary truth cannot possibly be false. It is true in all possible worlds. Examples:
All triangles have three sides.
All bachelors are unmarried.
No one who believes that God exists is an atheist.

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

6. Necessary Falsehoods
We can say similar things about necessary falsehoods.
Impossible to be true
Their falsity does not depend on what the facts are like; necessary falsehoods are always false no matter what

7. Necessary Truths and the A Priori
A Priori = prior to experience or independent of any experience of facts or states of affairs in the world.
Necessary truths are often said to be true a priori, true independent of any particular facts.

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

9. Necessary Truths and Analytic Truths
Necessary truths are sometimes called analytic truths
An analytic truth is necessarily true because
(1) Its predicate is contained in the concept of its subject.
(2) Denying the truth of the statement leads to a contradiction.
(3) Contradictions are impossible and go against reason.

10. Analytic Truths
“All sisters are female” is an analytic truth because the predicate “female” is contained in the subject “sister.” Why? A sister is defined as being a female sibling. So “All sisters are female” says the same thing as “All female siblings are female.” The predicate (female) is contained in the subject (female siblings). It is easy to see that it would be a contradiction to say that not all female siblings are female. So “All sisters are female” is necessarily true – it couldn’t possibly be false.

11. Analytic Truths Example: All fathers are males.
The concept “male” is in the concept of “father” (male parent).

12. Analytic Truths Example: All electrons are subatomic particles.
An electron is by definition a certain type of subatomic particle. So the concept of a subatomic particle is contained in the concept of an electron.

13. Empirical (or Contingent) Truths
Empirical = having to do with experience Contingent = depending on experience
A statement expressing an empirical truth is true in virtue of the facts. An empirical statement is empirical because its truth value (whether it is true or false) depends on what the world is like.

14. Empirical (or Contingent) Truths
Empirical Statement: Microorganisms live on Mars.
Empirical truth: Over 6 billion people live on Earth.
Empirical falsehood: Germany won WWII.

15. Empirical Truths and A Posteriori Truths
A posteriori = with experience or depending on experience of the facts
Empirical truths are sometimes called a posteriori truths because empirical truths depend on what the facts are like, and facts are known through some kind of sense experience.

16. Test: A Priori and A Posteriori: Are these statements true or false?
I can know a priori that all catholic priests are unmarried.
It is impossible to know a priori whether Milan has more inhabitants than Rome.
I can know a priori that there is life on other planets.
All of mathematics is based on a priori reasoning.

17. Necessary and Empirical Truths
Necessary Truths
Analytic
A priori
Empirical (or contingent) Truths
Synthetic
A posteriori

18. Can you KNOW any of the following? (Can you justify any?)
I know that I have two hands.
I know that president Napolitano will never get divorced.
I know that other people experience the smell of coffee just like I do.
I know that Totti is the better player of the Rome football team.
I know that water is H20.

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

22. Epistemic Justification
What can we know and how much do we know? To help answer these questions, we need a theory of epistemic justification. Knowledge is justified true belief. If we can determine when and how our beliefs are justified, then we can determine the scope and limits of our knowledge. In broad strokes, there are three main theories about epistemic justification:
(1) Skepticism
(2) Empiricism
(3) Rationalism

23. Skepticism
Skepticism says that there is no adequate justification for our beliefs, so we can never attain knowledge. We can have true beliefs, but no knowledge.
Global Skepticism denies that there can be knowledge of any kind about any subject matter. Not many people hold global skepticism, but it is hard to defeat in conversation
Local Skepticism denies that we can have knowledge regarding some subject matters, but not all, or that some methods of justification are not reliable (like reading fortune cookies, astrology, psychic hotlines, alternative medicine, or TV news).

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

25. Empiricism Criticism of rationalism
Necessary truths are just tautologies (true by definition or true analytically or true in virtue of logical form) and don’t say much about the world.
Rationalists produce absurd metaphysical claims about reality because they go too far and end up making bogus a priori claims that are also synthetic in order to say something meaningful about the world.

26. Empiricists John Locke (1632-1704) Bishop Berkeley (1685-1753)
David Hume ( )
John Stuart Mill ( )
Bertrand Russell ( )
Logical Positivists: A.J. Ayer ( )
William James ( )

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

28. Rationalists Plato could be called a rationalist
Rene Descartes ( )
Baruch Spinoza ( )
Gottfried Leibniz ( )

29. Empiricism
Empiricists believe that knowledge is acquired through sense experience.
So there has to be some theory of perception that connects sense experience with reality:
Whenever I perceive that object S has property P, S really has P.

30. Empiricism: 3 Theories of Perception
Naïve Realism
Representationalism
Idealism

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

32. Objection to Naïve Realism
It is not always the case that what I see is the truth. There is a difference between appearance and reality, and sometimes appearances are deceiving.
Illusions and mirages
People’s experiences differ: a wind may feel cold to me but warm to you. Who is correct?
The buckets-of-water example: Rest one hand in freezing water and one in hot water. Take both hands out and put them into a bucket of warm water. The water in the bucket will feel hot to the cold hand and cold to the hot hand. Which hand is giving the correct feeling?

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

34. John Locke: Theory of knowledge and Representationalism
We are born with minds that are like blank slates. There are no innate ideas. The view that there are innate ideas is dangerous and can be used to control people.
There are two sources of ideas: (1) sensation (sense experience of sense objects) and (2) reflection
The ideas of reflection are produced from the mind’s working on the ideas of sensation: perceiving, doubting, thinking, believing, reasoning, knowing, willing.

35. Locke: Knowledge and Representationalism
There are two kinds of ideas: (1) simple and (2) complex.
Simple ideas are those like the idea of the color yellow (from sensation) or the idea of pain (from reflection) that cannot be broken down into other ideas.
Complex ideas are made up of simple ideas. The mind can put simple ideas together to make a complex idea, like the idea of a golden mountain.

36. Locke: Knowledge and Representationalism
The mind creates complex ideas. The mind:
(1) joins ideas
(2) brings them together to compare them
(3) abstracts (abstract the idea of “man” from my experiences of John and Harry.)

37. Representationalism: Primary and Secondary Qualities
There are two kinds of qualities. A quality is the power in an object to produce any idea in my mind.
Primary qualities are those that really do exist in the bodies themselves. These include: Shape, Solidity, Extension, Motion or Rest, Number
Secondary qualities are those that do not really exist in the bodies themselves. These include: Tastes, Colors, Sounds, Odors, and certain Feelings of Touch, like softness or roughness.

38. Locke: Substance
Qualities do not just float around. They have to be in something. Something has to hold them together and organize them. The power to produce ideas in my mind has to be in something. This something is substance, which Locke takes to be matter.
Substance is matter, but we cannot say what it is because we never perceive it.

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

40. Berkeley: Idealism
Berkeley argues that if we are true empiricists, then we have to reject Locke’s idea of substance, or matter, because it is never perceived. Matter is a meaningless term.
Berkeley argues that there is no mind- independent substance. The existence of anything depends on a perceiving mind.
“Esse Est Percipi” – To be is to be perceived (by a mind).

41. Berkeley: Idealism
Rejects Locke’s distinction between primary and secondary qualities. There are no mind-independent qualities, no-primary qualities. Every quality is like a secondary quality. Every quality is experienced through a perceiving mind. Only sensed qualities are real.
“In truth, the object and the sensation are the same thing, and cannot therefore be abstracted from each other.”
Locke had removed beauty (and other secondary qualities) from the world. This made the world ugly.

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

43. Berkeley: Idealism
Another problem is that it seems that for anything to exist, it has to be perceived by a mind. But if a tree falls in the woods and no one is there to hear it, does it make a sound?
If we all close our eyes, does the world disappear?

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

45. Berkeley: Idealism
God is the source of our ideas. God is the mind that perceives all things. God is the (spiritual) substance behind all things.
God sees the tree fall, so it does make a sound.
Berkeley finds room for non-physical spiritual beings and rejects Locke’s materialism which seems to lead to atheism.

46. Berkeley’s Instrumentalism
The abstract ideas of scientists, like the ideas of force, attraction, and gravity, do not refer to anything real. Only sensed qualities exist. There is nothing other than what we can perceive. But these ideas are still useful ideas that can help us explain things. They just do not refer to anything real.
There is no causality. We never see that. Things just follow each other in time: A follows B, but it is never possible to say that A is the cause of B.
God orders the behavior of all things.

47. Hume: Empiricism
Explaining a similar empiricist view, Hume distinguished between (1) impressions and (2) ideas
Every idea comes from some impression from sense experience.

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

49. Hume: Empiricism and Skepticism
Hume thinks that if we are strict empiricists, then it is going to be very hard or impossible to answer these questions:
Is there an external world?
Can induction really work?
Can we ever know the ultimate substance?
Is there a self?
Is there causality (as necessary connection)?
Is there a God?