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What is Knowledge?True, Justified, BeliefNeeds to be ALL 3:
It can be true but not justified– you guessed correctly
Justification can be weak or strong…
Plato’s Tripartite Theory of Knowledge Meets Gettier’s ProblemAccording to Plato:A person S knows
proposition P if & only if:
P is trueS believes PS 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!
What do we know?Knowledge = justified true belief (Plato)The task:When are our beliefs justified?How are our beliefs justified?
Skepticism
• Beliefs can’t be justified
• We can have beliefs, but no knowledge
Rationalism
• Beliefs can be justified
• Justification comes from reason.
• Math & logic most reliable sources of knowledge
Empiricism
• Beliefs can be justified
• Justification comes from the evidence we receive from our senses
Descartes & SkepticismWanted 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…”
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’ malin génie 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?
SkepticismGenuine Knowledge is not
possibleAll we have are beliefsGlobal 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
Descartes’ MethodThe Method of DoubtReject any belief that
can be doubtedIf 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.
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
Cartesian CircleUse 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…..
Descartes’ LimitsInfers too much from
cogitoThinking 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
EmpiricismJustification for knowledge
comes from our sensesBasic 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
Inferential BeliefsThere 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
Justification of Inferential Beliefs If you can’t confirm or
falsify with evidence …then you should be
skeptical of this beliefExamples:
All men are created equal
God wrote the BibleEmpiricists tend to be
skeptical about religion &moral knowledge
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.
Primary and Secondary QualitiesSound 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
Primary QualitiesThe 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…
George Berkeley, critic of LockeAccepts
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?
Berkeley’s ImmaterialismReality 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
Berkeley & GodDo 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.
RationalismAgree with
Empiricists that knowledge is based on basic beliefs
BUT justification does not come from experience
Justification comes from Pure Reason
Math & RationalismWe cannot see, feel
or touch numbersSo if we have a
knowledge of numbers
This knowledge cannot be based on experience
Knowledge of numbers is based on Reason
Rational propositionsRationalists 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
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 sweetAll human beings have
the same fundamental rights
All cats are animalsIf any nation should
ever use nuclear weapons again, then millions of people will die
Types of Rationalist JustificationA prioriMeans from the formerUsed 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
carsAll triangles have 3 sides
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 particular tiger
A posteriori knowledgeAssociated with
EmpiricistsMeans from the
latterRequires that we
refer to specific experiences of the world
Example:There are 9 planets
in the solar systemDr. Ernst’s bike is
green
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.