The document discusses epistemology, the study of knowledge, defining it as justified true belief based on conditions proposed by Plato. It introduces concepts like necessary and sufficient conditions, presents the Gettier problem which challenges the tripartite definition of knowledge, and outlines the philosophical debates between rationalism and empiricism. Key figures such as Descartes, who proposed foundationalism and hyperbolic doubt, are examined, alongside the distinctions between a priori and a posteriori knowledge.

1. Epistemology
An Introduction to Philosophy: 02
© James Mooney 2012

2. What is epistemology?

3. What is Knowledge?
• A large part of philosophy involves coming
up with definitions.
• A definition of knowledge was first offered
by Plato in the Theaetetus.
• Plato’s account provided what he thought
were the necessary and sufficient
conditions for knowledge.

4. Necessary and Sufficient Conditions
Definitions in philosophy are often offered in terms of necessary and sufficient
conditions.
A necessary condition is something that must hold in order for something to be
the case.
E.g. It is a necessary condition of being a human that you are a
mammal, but this is not sufficient.
A sufficient condition is something that assures that something is the case.
E.g. It is a sufficient condition for being a mammal that you are a
human, yet it is not necessary.
It is usual for definitions to be stated in terms of individually necessary and
jointly sufficient conditions.
E.g. A necessary condition for being a sister is that you are female.
However,thisaloneisnotsufficientforsisterhood;itisalsonecessary
that you be a sibling. As such there are two individually necessary
conditionsforbeingasisterandthesearejointlysufficient.Therefore,
we can define a sister as a female sibling.

5. What is knowledge?
• There are generally thought to be 3 individually
necessary and jointly sufficient conditions for
something to count as knowledge.
1. Belief condition: in order for (x) to know (p), (x)
must believe that (p).
2. Truth condition: in order for (x) to know (p), (p) must
be true.
3. Justification condition: in order for (x) to know (p),
(x)’s true belief that (p) must be justified in some
way.
• As such, we can define knowledge as justified
true belief (JTB); thus, if one has a knowledge
one has a JTB, and if one has a JTB one has
knowledge.

6. What is knowledge?
The Gettier Problem
Jennifer believes that Brad is having an affair with Angelina and, in
fact, it’s true that Brad and Angelina are having an affair.
Jennifer’s suspicions were aroused by the fact that the paparazzi
photographed the pair together in a restaurant on a night when Brad
had said that he was busy filming. As such, Jennifer’s belief is
justified. However, what Jennifer doesn’t know is that Angelina
was actually out with a Brad impersonator that night (Brad was
actually filming and Angelina was so besotted that she hired a look-
alike). So Jennifer has a justified true belief that Brad and Angelina
are having an affair, but does she have knowledge? Does Jennifer
know about Brangelina?
• Examples like this (Gettier-style counterexamples),
which problematize the tripartite definition of knowledge
as JTB, have been common since Edmund Gettier’s
hugely influential 1963 paper ‘Is knowledge justified
true belief?’.

7. What can we know?
René Descartes
1596-1650
Father of Modern
Philosophy
Cogito ergo sum

8. What can we know?
Background to Descartes
• Medieval hierarchy of knowledge
1. Revelation
2. Authority
3. Reason
4. Observation
• The Scientific Revolution
The new science of Copernicus, Galileo, etc. contradicted some of the
central claims of Christianity (geocentricism, etc.). As such, there is
an intellectual crisis prompting some sceptics to claim that knowledge
is impossible.

9. What can we know?
Meditations on First Philosophy (1641)
Descartes’ Aim:
‘to demolish everything completely and start right again from the
foundations.’
Descartes’ Method
1. Hyperbolic (Cartesian) doubt
Descartes’ ‘method of doubt’ entails that if anything can be doubted,
however slightly, then we are to treat it as if it is manifestly false and
reject it outright.
2. Foundationalism
Descartes will not subject each and every one of our opinions to this
hyperbolic (exaggerated) doubt, as this would be a Sisyphean task.
Rather, Descartes aims to test the ‘foundations’ of what we claim to
know - ‘as the removal from below of the foundation necessarily
involves the downfall of the whole edifice’. Descartes identifies the
first potential foundation for knowledge as experience derived from
the senses.

10. What can we know?
Dream Hypothesis (Meditation I)
‘There are no certain signs by which we may clearly distinguish
wakefulness from sleep.’
– The fact that I cannot be certain that I am not now dreaming gives
us reason to doubt the reliability of the senses.
– If something can be doubted then it ought to be treated as if
manifestly false.
– This entails that all claims that are grounded on the reliability of
the senses are open to doubt.
– The entire class of beliefs that depend upon the senses must,
therefore, be treated as if manifestly false.
Having dispensed with experience, Descartes next turns his mind to an
alternate foundation for knowledge - reason:
– ‘for whether I am awake or dreaming, it remains true that two
and three make five, and that a square has but four sides’.

11. What can we know?
Demon Hypothesis (Meditation I)
‘I will suppose… that some malignant demon, who is at
once exceedingly potent and deceitful, has employed all
his artifice to deceive me.’
– In this way, Descartes puts pay to the realm of that gained through
reason in like manner to that derived from sense experience.
– In case you find the introduction of a malevolent genie too much to
bear, Hilary Putnam (Reason, Truth, and History, 1981) updates
the argument by asking you to consider the possibility you are a
brain in a vat and that your experiences are just electronic signals
being sent to your disembodied brain by an evil scientist. This
thought experiment also forms the plot of the Hollywood
blockbuster The Matrix.

12. What can we know?
The Cogito
At the outset of Meditation II Descartes states that:
‘The Meditation of yesterday has filled my mind with so many doubts, that it
is no longer in my power to forget them... I suppose, accordingly, that all the
things which I see are false (fictitious); I believe that none of those objects
which my fallacious memory represents ever existed; I suppose that I possess
no senses; I believe that body, figure, extension, motion, and place are merely
fictions of my mind. What is there, then, that can be esteemed true? Perhaps
this only, that there is absolutely nothing certain.’
In order to progress, he must establish one thing that is certain and
indubitable. This eventually leads him to the cogito:
‘this proposition I am, I exist, is necessarily true each time it is
expressed by me, or conceived in my mind.’
The cogito delivers subjective certainty; I can be sure of how things
seem to me. The challenge for Descartes and his successors is how, if
at all, we can move from subjective to objective knowledge of the
world.

13. How can we know?
Rationalism
• Descartes is a Rationalist. Rationalists believe that knowledge
can be acquired by reason alone, without recourse to
experience. Such knowledge, it is claimed, must somehow be
present in the mind at birth (innatism).
– In fact Descartes depends upon an innate idea of God (the
trademark argument) in attempting to escape the demon
hypothesis.
• Knowledge which is known via reason alone is called a priori.
– E.g.1. ‘2+2=4’
• Analytic propositions, which are made true (or false) by the
meanings of their terms alone, are known a priori.
– E.g.2. ‘All brothers are male’
• All a priori truths are necessary - they could not possibly be
false; they must be true.
– E.g.3. ‘Either Jim is in Edinburgh or he is not’

14. How can we know?
Empiricism
• In opposition to Rationalists like Descartes are the Empiricists;
for example, John Locke (1632-1704) and David Hume
(1711-1776). Empiricists believe that knowledge depends upon
experience derived from the senses. As such, the mind is a
‘tabula rasa’ at birth; innatism is false.
• Knowledge which is derived from sense experience is called a
posteriori.
– E.g.4. ‘There are four men in the classroom’
• Such propositions are said to be synthetic as they are not true
(or false) due to the meaning of their terms alone (they
synthesise different concepts).
– E.g.5. ‘Jim has a brother’
• All a posteriori claims are contingent - even if true, they might
possibly have been false.
– E.g.6. ‘Jim is in Edinburgh’

15. How do we know what we know?
• Rationalism
• Empiricism
– A priori knowledge
– A posteriori knowledge
– Analytic
– Synthetic
– Necessary
– Contingent
The problem, an empiricist will claim, is that whilst a priori/
analytic knowledge delivers certainty, it is actually rather
trivial and worthless. The knowledge that we actually want
about the world is of the a posteriori/ synthetic type.
However, the Rationalist will respond, this ‘knowledge’ is far
from certain.

17. Details
James Mooney
Open Studies
The University of Edinburgh
j.mooney@ed.ac.uk
www.filmandphilosophy.com
@film_philosophy