Three Theories of Knowledge

1. Three Theories of Knowledge Skepticism, Rationalism & Empiricism

2. What is Knowledge? • True, Justified, Belief • Needs to be ALL 3: • It can be true but not justified– you guessed correctly • Justification can be weak or strong…

3. Plato’s Tripartite Theory of Knowledge Meets Gettier’s Problem • According to Plato: • A person S knows proposition P if & only if: • P is true • S believes P • S is justified in believing P • Gettier offers examples where: • Someone forms a belief that is true & justified • BUT does not qualify as knowing what they think they know • Holding a truth can sometimes be luck!

4. What do we know? • Knowledge = justified true belief (Plato) • The task: • When are our beliefs justified? • How are our beliefs justified?

5. Descartes & Skepticism • Wanted to prevent skepticism from undermining all claims to knowledge • Product of Reformation & Scientific Revolution • Is he a skeptic? • He does not want to be one… • I noticed that while I was trying to think every thing false, it was necessary that I, who was thinking this, was something. And observing that this truth, “I am thinking, therefore I exist” was so firm and sure that all the most extravagant suppositions of the skeptics were incapable of shaking it…”

6. The Brain in the Vat & the Evil Demon in Your Mind • What if you are just a brain in a vat, connected to a computer that causes you to think that you are living a ‘normal’ life? (Hilary Putnam, 1981) • Is everything you think about the world wrong? • Descartes’ malingénie puts wrong ideas in your head… how do you know what is true or real? • Descartes says: cogito ergo sum • Putnam says the scenario is illogical because the envatted brain is invisible & indescribable from within… • Convinced?

7. Skepticism • Genuine Knowledge is not possible • All we have are beliefs • Global skepticism = no knowledge of any kind is possible • Local skepticism = there are some things we cannot know • Some ways of acquiring beliefs cannot bring knowledge (dreams, psychics, astrology) • The computer is so clever that it can even seem to the victim that he is sitting and reading these very words about the amusing but quite absurd supposition that there is an evil scientist who removes people’s brains from their bodies and places them in a vat of nutrients. ~Hilary Putnam, Reason, Truth & History 1981

8. Descartes’ Method • The Method of Doubt • Reject any belief that can be doubted • If an evil-demon is deceiving you, any of your ‘truths’ could be wrong • What is left? • Your mind! The evil demon…will never bring it about that I am nothing so long as I think that I am something.. I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind.

9. Descartes’ Limits • Infers too much from cogito • Thinking is going on, but who is doing the thinking? • Limited to the first person • Demon could trick me into thinking you are thinking • Limited to present tense

10. Can we Rebuild? • Knock down the faulty foundation, but then what? • Descartes concludes that the things we see very clearly & distinctly are true • Why? • God

11. Descartes & God • God is perfect, all-powerful & all-knowing • The source of all our ideas • Because he is good, he will not deceive us • God leads us to the truth

12. Cartesian Circle • Use clear & distinct ideas to prove existence of God • God gives us clear & distinct ideas • We use those ideas to prove the existence of God • God gives us clear & distinct ideas…..

13. Empiricists • British response to Continental Philosophers • John Locke • George Berkeley • David Hume

14. Empiricism • Justification for knowledge comes from our senses • Basic empirical beliefs are directly derived from experience • They are therefore justified & count as evidence • Example of a basic empirical belief: • I see a red phone • & so I believe there is a red phone in front of me

15. Inferential Beliefs • There are beliefs about things that are NOT directly observable • Example: dinosaurs once existed • Can see them or touch them now • Inferential beliefs: bones, archaeological remains

16. Justification of Inferential Beliefs • If you can’t confirm or falsify with evidence • …then you should be skeptical of this belief • Examples: • All men are created equal • God wrote the Bible • Empiricists tend to be skeptical about religion &moral knowledge

17. John Locke • Locke says: • Human understanding is like a closet wholly shut from light, with only some little openings left, to let in external visible resemblances, or ideas of things without.

18. Primary and Secondary Qualities • Sound skeptical? • Locke has a solution… • Our perception might be unreliable, but it depends on what type of qualities we are perceiving… • Take the red tomato… • It’s redness is a product of the interaction of various factors (texture, surface, our sensory system, environment at the time) • These properties don’t belong to the tomato • Therefore secondary qualities

19. Primary Qualities • The tomato has some true qualities: size & shape • These do not depend on the conditions under which it is observed • Does not even require an observer • These are primary qualities • Locke thought primary qualities were proof against the skeptics doubts…

20. George Berkeley, critic of Locke • Accepts representational model of perception • i.e.- seen objects are ideas • But, he asks, how could you check on all this if you are in Locke’s closet?

21. Berkeley’s Immaterialism • Reality consists in the ideas or sensations themselves • We are fully & properly connected with these! • Skepticism averted! • But… wait, is anything real? • Berkeley says: to exist is to be perceived

22. Berkeley & God • Do things cease to exist the moment we stop looking at them? • Berkeley says: • Everything is conceived all the time in the mind of God • So, the continual existence of the world is assured • All the choir of heaven and furniture of earth - in a word, all those bodies which compose the frame of the world - have not any subsistence without a mind.

23. Rationalism • Agree with Empiricists that knowledge is based on basic beliefs • BUT justification does not come from experience • Justification comes from Pure Reason

24. Math & Rationalism • We cannot see, feel or touch numbers • So if we have a knowledge of numbers • This knowledge cannot be based on experience • Knowledge of numbers is based on Reason

25. Rational propositions • Rationalists say… • When we think about certain propositions we can quickly see that they are true • These propositions have something self-evident about them • Simple reflection shows that these propositions (beliefs) are likely to be true I believe that, if a triangle could speak, it would say... that God is eminently triangular, while a circle would say that the divine nature is eminently circular… ~ Baruch Spinoza

26. You be the Rationalist… True? Or False? • If one multiplies any natural number by 2 then the resulting number is even • The income of the average worker in the US is higher than the income of the average worker in Europe • Every state must have some form of government • Every event has a cause. • Sugar is sweet • All human beings have the same fundamental rights • All cats are animals • If any nation should ever use nuclear weapons again, then millions of people will die

27. Types of Rationalist Justification • A priori • Means from the former • Used to refer to a justification that can take place prior to consulting empirical knowledge • You can know something a priori if you can know it without 1st seeing, touching or hearing anything in particular • Examples: • All red cars are colored cars • All triangles have 3 sides

28. A priori doesn’t mean “no experience necessary”… • Just not any particular experience • Example: • In order to know that tigers are animals… • I might have to look at a picture or see some • BUT I don’t have to see any particulartiger

29. A posteriori knowledge • Associated with Empiricists • Means from the latter • Requires that we refer to specific experiences of the world • Example: • There are 9 planets in the solar system • My bike is green.

30. True or False? • I can know a priori that all bachelors are not married • A fully committed empiricist holds that all our knowledge is justified a posteriori. • It is impossible to know a priori whether New York has more inhabitants than Mexico City. • I can know a priori that there is life on other planets. • I can know a priori that if somebody is hot to death then somebody must have been the shooter. • I can know a priori that all swans are white. • All of mathematics is based on a priori reasoning.