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The Problem of Knowledge of the External World

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Tim Fisher

on 27 April 2016

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Transcript of The Problem of Knowledge of the External World

Discuss the following questions with your group
1. What do you know? How do you know it?
(It may be easiest to think of one or two things that, as a group,you are certain you know. Decide how you know it and why you are certain you know it!)
But, wait. What is knowledge?
When we say we "know" something, what are we saying?
Are there necessary and sufficient conditions for knowledge?
I "know" your younger brother, Thomas.
I "know" how to bake cookies.
I "know" that there is a chair in this room.
Knowledge =

A belief
That is true
And justified
How much justification?
Gettier objections
Problem of regression.
Circular justification
Belief A
Belief B
Belief C
Causal Theory
Belief must be true
Belief must be caused by the thing that makes it true.
OR, there must be an appropriate causal chain (dinosaurs)
BUT, again, issues:
Have to believe in the cause!
We need not worry too much!
Let's just say for our purposes that knowledge is:
a true belief for which we have some justification for believing.

What do we know?
When and how are our beliefs justified?
What can we say we know about the external world?
... small
Three theories of knowledge
there is no adequate
justification to establish
our beliefs are true
we can know things
if we can justify them with reason and knowledge (sense knowledge is not reliable)
only beliefs that we can
justify by our senses can be established as true
Rene Descartes
I think therefore I am
Can I have knowledge of the external world?
Through senses?
Through reason?
Evil Demon
Innate ideas
Reason and senses
are therefore reliable
Problems with Descartes:

1. Does he doubt everything?
2. Ontological / argument / trademark arguments dubious
3. "Cartesian Circle"

Perhaps, at best, Descartes has proof for a kind of solipsism
Basic empirical belief - beliefs derived directly from sensory experience. (These count as evidence!)
Inferential belief - beliefs based on things not directly observable but which are justified with reference to basic empirical beliefs.

Any belief that cannot be confirmed or falsified by a basic empirical belief is not knowledge.

2. Induction
Can empiricism allow us to make general claims about the world - claims that are beyond what we could (even as a species) experience?
e.g. The ocean is full of salt water.

1. Perception
“Whenever we perceive an object O (like a banana) to have the property P (like being yellow) are we justified to believe that O really does have property P?
So, is the external world really the way we perceive it to be?: three theories of Perception

1 - Naive Realism / direct realism / common sense realism: the world is exactly as we perceive it.

2 - Indirect Realism / Representative Realism: not all properties we perceive in an object are actually there (JOHN LOCKE)

3 - Idealism: objects are only a collection of our perceptions, not independent from our minds (George BERKLEY / HUME)
Problem of Induction:

We cannot observe the future!
To claim inferences are reliable is impossible without some level of circular argument.

1. All dolphins observed in the past 10 years mate for life (PS. no idea if this is true!!)
THEREFORE: All dolphins mate for life.

How do we jump from premise 1 to the conclusion? Well, because of some idea like this:
nature acts in uniform and predictable ways.

Ok, BUT, how do we know this?? This is ITSELF an inference... we are in a circular argument.
Beliefs are justified by pure reason - independent of experience.
When we think about certain propositions we can figure out if they is true (without any need for experiene)
e.g. 3 is bigger than 1; babies are younger than adults; all black shoes are colored black.
we call this a priori
as oppossed to a posteriori
Analytical truth: true by virtue of the meaning of the words involved. (All oakes are trees)
Synthetic truth: we need to conduct an experiment or observe. (Oak trees grow taller than daffodils)
Sharp objects are painful if you touch them. However, we do not think that 'painful' is a property of the object. Why, then, should all the other sensations that arise in us when we interact with objects be properties of the objects?
Galileo: Primary qualities are properties of the objects. Secondary qualities are purely in us, and nothing to do with the object at all.

Locke: Primary qualities are those properties of the object that cause a sensation in us which resembles the property in the object. Secondary qualities are those properties that cause a sensation in us which does not resemble the property in the object.
Which properties are primary, and which secondary? There are a few ways to draw the line.
Properties which would exist even if the object were always unobserved are primary.
Properties which would exist even if the object were the only thing in the universe are primary.
Properties, like shape, which we can detect with two or more senses are primary.
If we could be completely mistaken about a property and still function, that property is secondary.
Why expect the sun to rise tomorrow??
1. inductive arguments do not guarantee the truth of a conclusion.
2. induction rests on an unjustified assumption ...
3. ... nature is uniform!
4. We cannot observe nature at all times and all places ... we have to make an inference!
5. This is circular!

A Priori Knowledge – “Some ideas are true independent of experience”.
a. Mathematical propositions (2 + 2 = 4).
b. Things which are true by definition (all bachelors are unmarried).
c. Self-evident truths (such as “I think therefore I am” or “God exists”).
Innate Ideas – “Some ideas are present from birth”.
Logical Necessity – “Some things cannot be conceived of as otherwise”.
Problems - synthetic V analytical truths ....
Sentences that express analytical truths are simply true - true because of the meaning of the words in the sentence.
Belief A
Belief B
External World
How / Can we be confident that the external world is the way we perceive it to be? How do I know that there really is a chair, that is red, 'out there'?
Do exercise 2
Destructive phase (Cartesian doubt)
Constructive phase
trademark argument
ontological argument
God exists.
God is all-good.
An All-good God would not deceive us. (That would be malicious)
Cartesian Dualism
definitely a finger!
Do exercise 5

Make a list of things which are a simple idea, a complex idea, or (according to the empiricist) cannot be known.
1. How plausible is the central premise of the movie?
2. How do you know you are not, right now, in the Matrix?
3. Everything in the Matrix is false. Are there limits to what humans can be fooled into believing is real?
4. If you had choice between being kept in ignorance and living in the Matrix, or being told the truth - even if the truth was a nasty dystopia - which would you chose?
What are some of the explanations for seeing a red chair?
Empiricism and Knowledge of the External World
1. I see a red chair because there really is a red chair 'out there.'
2. I see a red chair because there is something that is chair sized and shaped, but the 'red' is merely created by my perception
3. I see a red chair because my chemical-electro impulses are stimulated in my brain etc. BUT there is no chair 'out there' at all.
Exercise 3
if there is any reason to doubt a claim, it cannot be knowledge
my quest is for things we know for certain: foundational knowledge.
methodological doubt
necessary truth: something we know is true without the need for any reference to the actual world.
contingent truth: something is contingently true if the truth depends on how the actual world is.
exercise 3
exercise 4
1. My sense are sometimes fooled.
2. For all I know, at any given moment, all my sensory information about the world could be wrong.
3. My rational/logical thought could be being manipulated, and so wrong.
Certainty seems far too strong a criteria for knowledge.
This is the classical definition of knowledge
So, we can have the ideas of redness, roundness, sweetness as a direct result of experiencing those things.
We could not have these ideas without experience
! We cannot create them ourselves
We can the combine those basic ideas to have an idea of a tomatoes, without having to experience a tomatoes.
By contrast, Rationalists - like Descartes - agree that there are some things we can never have experience of, but claim that we know these things because they are INNATE IDEAS. Empiricists deny such innate ideas - tabula rasa
Descartes Epistemology
some jargon
a priori - knowledge independent of experience ("all bachelors are unmarried.")

a posteriori - knowledge dependnt on experience ("some bachelors wish they were married.")
Exercise 2
Belief .V. Knowledge
Make two lists. One should be of things you believe are true. One should be of things you know are true.
Here are some things to include, to get you going:
that I am a human being
that the earth is round (well, an oblate spheroid)
that the Yankees will win the World Series
that ice is cold
that my parents love me

Cartesian Doubt

Decide if you have reason - even the slightest reason - to doubt the following statements are true. Why?
There is a tree outside
I am currently in a philosophy class.
I have two arms.
I graduated from High School
Oranges are, well, orange.
Triangles have three sides
100 + 3 = 103

Is there anything (anything else) that you believe you know for certain?

Q. Descartes proposed that each of us (from our own perspective) cannot be sure that we are not, right now, dreaming. How might you respond to this? How might you argue that you are not dreaming?

Q,. Even if our senses are not a reliable basis for knowledge, might our logic (a priori reasoning) be? Why, why not?
Drawing game
knowledge requires certainty
Simple ideas (direct experience of)
Complex Idea
All bachelors are male
All pigs are pink
Logical truth.
Need to consult world to verify truth
Tells us nothing about how the world is!
Informs us about the world
Describe each of the following in terms of primary and secondary properties.
Perceptions cannot always be a true reflection of how the real world is... we are not directly aware of the external world.
1. What we see is bent.
2. The pencil is not bent.
3. So what we see is not the pencil.
What we see is SENSE DATA... the content of our sensations.
Seems we are trapped behind the "veil of perception" (Locke).
If all we ever get is sense data, how can we know what the world is actually like?

Representative Realism
1. sensations are caused by external objects
2. at least some of our sense data resembles those objects
time lag argument
1. What is more important, nature or nurture?
2. What does it mean when we say something is 'red'?
3. When Tommy sees a cat, what is happening?
Opening Puzzlers
What is the difference
between something we
believe, and something we know?
The Problem
How certain can we be that the external world is exactly as we perceive it to be?
The Problem
Exercise 5
since our senses sometimes deceive us, it is prudent never to trust them (completely).
1. We can't be certain that we are not dreaming
2. If we can't be certain that we are not dreaming, we cannot be certain that what we sense is real.
3. If we can't be certain that what we sense is real, we cannot acquire knowledge through sense experience.
THEREFORE: we cannot acquire knowledge through sense experience.
1. When we reason that 7 + 3 = 10 there are 2 possibilities about what is going on.
(i) Our reason is reliable. We do the calculation correctly. And 7 + 3 does = 10.
(ii) An evil demon is manipulating our thoughts. We come to 'see' that 7 + 3 = 10 only because he is putting that idea into our minds. We are being deceived.
2. We can trust our power of reason ONLY if we can rule out (ii) above.
3. We cannot rule out (ii).
THEREFORE: our power of reason is not, by itself, a reliable source of knowledge... it cannot be trusted naively.
our senses and our powers of reasoning can not be taken as reliable... unless I can give an argument that shows there is good reason why they can be taken as reliable.
I need a foundation
from which to build...
Is there anything I can 100% be sure of... anything that cannot be doubted?
Rational thinking
Existence of God
Cartesian Circle
Henry holds the following assertions to be absolutely and indubitably true. He believes with total certitude that these assertions are true. There is not a shred of doubt in his mind about any of them, and he thinks that anyone who could doubt, even for a minute, the truth of assertions like these must just be really stupid, or a total fool, or maybe insane.

(i) consider what the foundation of Joe's beliefs about these things might be. How does he know they are true? (been told? immediate experience? Remembers the event etc.)

(ii) what could be some possible areas of potential doubt with regard to these specific beliefs. In other words, what might Henry not be considering about his beliefs that could make these assertions, in fact, potentially untrue?
1. Someone tells you.
2. What some 'authority' says.
2. You remember it.
3. Immediate experience of it.
4. Rationally: you work it out.
Exercise 1.2
Exercise 1.1
SO, what is knowledge?
Exercise 3: Gettier
Exercise 2
caveat #1 You personally do not have to had experienced the thing ... if I read about something that someone else experienced, that counts! (e.g. I can say I know?)
caveat #2 We can still use our mind and powers to think and know things in this regard. Locke called this reflection. So, I can know about my own mental processes ... "remembering" etc.
#3 We can still know about somethings we could not actually have experienced because we can reflect on the evidence we do experience. For example:
founder of British Empiricism
We know something if - and only if -we can justify it through our senses. That is, if we can come to know it through experience.

All knowledge starts with a sensory experience.
A bit like lego ...
You can make lots of things with lego but you need the basic building blocks.
Locke said these basic building blocks were ideas only obtainable through our senses.
Locke also said you cannot build anything without these basic blocks.
So, knowledge depends on sensory experience.
Simple and Complex ideas
Because there is a time lag in creating a mental perception of something we see/hear etc., what we see/hear etc. is NOT identical with the world.
Perception is merely a mental image of the world.
Bertrand Russell
So, what about these two issues:
we cannot experience every single incident of many many claims. For example, no human has experienced every snake and yet we say we know snakes have no fur.
even more clearly, we cannot possibly experience future. Yet, we cay we know that, when I throw a ball, it will eventually fall to earth?
We make inferences.

We make inferences!
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