1. Epistemology
What do we know and how do we know it?
George Matthews
Spring 2016

2. What is knowledge?

3. What is knowledge?
To know something is to have a belief that is true and to
have a justification or good reason to believe it.
the standard definition

4. What is knowledge?
To know something is to have a belief that is true and to
have a justification or good reason to believe it.
the standard definition
! We often think of knowledge as the opposite of belief.

5. What is knowledge?
To know something is to have a belief that is true and to
have a justification or good reason to believe it.
the standard definition
! We often think of knowledge as the opposite of belief.
! But since we must also believe what we know, knowledge is
really a type of belief that has something more than “mere
belief.”

6. What is knowledge?
To know something is to have a belief that is true and to
have a justification or good reason to believe it.
the standard definition
! To know something is to have a belief that is also true.

7. What is knowledge?
To know something is to have a belief that is true and to
have a justification or good reason to believe it.
the standard definition
! To know something is to have a belief that is also true.
! Nobody really knew that the earth was flat – firmly held
belief in a falsehood isn’t knowledge.

8. What is knowledge?
To know something is to have a belief that is true and to
have a justification or good reason to believe it.
the standard definition
! To know something is to have a belief that is also true.
! Nobody really knew that the earth was flat – firmly held
belief in a falsehood isn’t knowledge.
! There is a difference between thinking you know something
and actually knowing it.

9. What is knowledge?
To know something is to have a belief that is true and to
have a justification or good reason to believe it.
the standard definition
! Part of the difference involves having a good reason to
believe what you claim to know.

10. What is knowledge?
To know something is to have a belief that is true and to
have a justification or good reason to believe it.
the standard definition
! Part of the difference involves having a good reason to
believe what you claim to know.
! Thus we must also have a justification for a true belief to
count as knowledge.

11. What is knowledge?
To know something is to have a belief that is true and to
have a justification or good reason to believe it.
the standard definition
! Part of the difference involves having a good reason to
believe what you claim to know.
! Thus we must also have a justification for a true belief to
count as knowledge.
! Lacking justifications our true beliefs would just be lucky
guesses.

12. What is knowledge?
To know something is to have a belief that is true and to
have a justification or good reason to believe it.
the standard definition
NOTE: defining knowledge in this way does not
guarantee that we actually have any knowledge,
it just sets a standard that we must meet in
order to legitimately claim to know something.

13. Plato’s Rationalism
Plato: 428 - 348 BCE
What we encounter in experience is an
imperfect manifestation of a more perfect
reality graspable by the mind alone.

14. Plato’s Rationalism
Plato: 428 - 348 BCE
If we see two square objects and conclude that they
are equal in size we must rely on concepts like
SQUARE and EQUALITY which we couldn’t pos-
sibly have gotten from experience since no perfect
squares or exactly equal things exist in the world of
our experience.

15. Plato’s Rationalism
Plato: 428 - 348 BCE
The philosopher pursues wisdom by attempting to
grasp these perfectly rational and ideal Forms mani-
fest imperfectly in the world. Only after death will the
soul encounter such Forms directly, once it is freed
from the limitations of the body.

16. Plato’s Rationalism
Plato: 428 - 348 BCE
For Plato learning is actually recollection of
ideas of the Forms already imprinted on the
mind at birth.

17. Plato’s Rationalism
Plato: 428 - 348 BCE
Plato is a rationalist in that he thinks that reason
takes priority over experience in attaining knowledge.
His views greatly influenced Christianity via the “neo-
Platonists” who equated contemplation of the Plato’s
Forms with contemplation of the divine principle gov-
erning the universe.

18. Descartes’ Rationalism
Rene Descartes: 1596 - 1650
We do not have direct experience of
reality but instead represent reality in
our thoughts. The only guarantee that
these representations are accurate is some
set of thoughts that cannot be doubted.

19. Descartes’ Rationalism
Rene Descartes: 1596 - 1650
Descartes relies on the method radical doubt to clear
away all ideas that are less than certain in search of
a sound foundation for knowledge.

20. Descartes’ Rationalism
Rene Descartes: 1596 - 1650
He is thus led to wonder how he can tell whether he
is awake or dreaming or even completely deceived by
a massive illusion. He finds that the only thing that
is certain is that as long as he is thinking or doubting
he must exist – cogito ergo sum or “I think, therefore
I am.”

21. Descartes’ Rationalism
Rene Descartes: 1596 - 1650
But if he can be sure only that he himself exists, how can he
find a way out of solipsism, locked inside his own head un-
certain of anything “outside”? To find a way out Descartes
relies on an argument that shows that a God exists who
would never let him be deceived as long as he relies only
upon “clear and distinct ideas” as the basis for claims about
the world.

22. Descartes’ Rationalism
Rene Descartes: 1596 - 1650
But Descartes’ argument has struck many people as
being circular. We rely on clear and distinct ideas to
prove that God exists, but God’s existence is required
for us to be able to trust that clear and distinct ideas
are in fact reliable.

23. Locke’s Empiricism
John Locke: 1632 - 1704
The mind at birth is a blank slate
– experience is our sole source
of knowledge about the world.

24. Locke’s Empiricism
John Locke: 1632 - 1704
Locke sets out to provide an account of the origins
of all knowledge about the world, both particular and
general ideas, in direct experience. For Locke we start
out knowing nothing and acquire all our knowledge
through experience.

25. Locke’s Empiricism
John Locke: 1632 - 1704
Locke was arguing against those rationalist philosophers
like Descartes who claimed that we had certain “innate
ideas” built in to our minds. So he sets out to show
how even the most abstract ideas like SUBSTANCE are
really attained in experience.

26. Locke’s Empiricism
John Locke: 1632 - 1704
Many later philosophers felt that Locke’s attempts to show
how abstract concepts were derived from experience did not
really work. For rationalists his argument assumes that we
already know what these concepts mean, while for empiri-
cists, they remain too abstract to really have been derived
from experience.

27. Berkeley’s Idealism
George Berkeley: 1685 - 1753
To be is to
be perceived.

28. Berkeley’s Idealism
George Berkeley: 1685 - 1753
Berkeley defends a rather strange sounding claim, that
since we cannot make sense of what something would be
like without actually perceiving it or imagining that we are
doing so, we should stop assuming that anything can have
an existence apart from being apprehended by some mind.

29. Berkeley’s Idealism
George Berkeley: 1685 - 1753
On this view a tree falling in the forest with no one
around to witness it not only doesn’t make a sound,
it doesn’t even exist.

30. Berkeley’s Idealism
George Berkeley: 1685 - 1753
By why then do things seem to persist in between
times we perceive them? Berkeley answers that there
must be a mind perceiving things to keep them in the
same state from one moment to the next and this
mind is the mind of God.

31. Berkeley’s Idealism
George Berkeley: 1685 - 1753
Berkeley is led to this extreme conclusion by thinking through
the basic empiricist idea that our knowledge comes from our
experience alone – outside of experience we can say nothing
about objects, hence objects that are not objects of someone’s
experience are meaningless.

32. Hume’s Skeptical Empiricism
David Hume: 1711 - 1776
All of our knowledge claims are either claims
about ideas and their definitions, or claims
about particular experiences. So generalizing
about experience is always hazardous.

33. Hume’s Skeptical Empiricism
David Hume: 1711 - 1776
Hume was interested in applying the scientific method to
the study of human beings and was thus the first mod-
ern cognitive psychologist. Today he is most known for
his skepticism about abstract concepts like CAUSATION,
SUBSTANCE and SELF.

34. Hume’s Skeptical Empiricism
David Hume: 1711 - 1776
For Hume all concepts we use to talk about what we experi-
ence should themselves be based on direct experiences. But,
with causality for example, we never actually experience one
thing causing another, instead we see one thing happen and
then another. So we should give up the general idea of cau-
sation in his view.

35. Hume’s Skeptical Empiricism
David Hume: 1711 - 1776
Likewise with the concept of a SELF or soul underlying and
unifying our experiences and our personalities. Each of us
experiences a series of particular events, but never do we
encounter a SELF or soul having those experiences.

36. Hume’s Skeptical Empiricism
David Hume: 1711 - 1776
Hume’s epistemology is based on his claim that all knowledge
must either be a matter of the definitions of words or direct
experiences. But is this claim itself something he knows by
definition or that he could have gotten from experience? It
seems to be neither, so how can Hume claim that it is true?

37. Kant’s Constructivism
Immanuel Kant: 1724 - 1804
Instead of assuming that our
knowledge must conform to objects,
we should suppose that objects must
conform to our cognitive powers.

38. Kant’s Constructivism
Immanuel Kant: 1724 - 1804
Kant responded to the debate between the empiricists
and the rationalists by saying that both were right in
certain ways and both wrong in other ways.

39. Kant’s Constructivism
Immanuel Kant: 1724 - 1804
The empiricists were right in that the content of our knowledge
about the world certainly comes from experience. In addition,
the fact that philosophers get caught in endless debates about
freedom, immortality, the soul, God, whether the world is finite
or infinite, shows that our knowledge cannot extend beyond
what we are capable of experiencing.

40. Kant’s Constructivism
Immanuel Kant: 1724 - 1804
The rationalists, however, were right in that the mind provides
an a priori structure to experience. The general concepts we
use to organize and make sense of experience are built in to
the mind. Hence we cannot help by see one thing as causing
another, a unified world of things organized in space and time,
and possessing an internal identity that allows them to persist
through time.

41. Kant’s Constructivism
Immanuel Kant: 1724 - 1804
Kant’s conception of knowledge as a combination of empirical
content and a priori structure has been central to all post-
Kantian philosophy and the field of cognitive psychology. The
big question is whether this structure is universal and common
to all rational beings, as Kant thought, or variable among
different cultures, genders or even individuals. Maybe there is
a bit of both – perhaps we all share certain basic concepts,
but then other aspects of our experience are variable.