Rationalism and Empiricism
Rationalism and Empiricism
Two Kinds of Truths
Before discussing the philosophers, it will
be helpful to begin by explaining an
important view about how statements (or
truths) can be classified into two main
types. This distinction is important
because it can help us understand the
difference between rationalists and
Two Kinds of Truth
Traditionally, there are two kinds of
(1) NECESSARY (also called truths of
(2) EMPIRICAL (also called contingent
truths or truths of fact)
A statement expressing a necessary truth
cannot possibly be false. It is true in all
possible worlds. Examples:
All triangles have three sides.
All bachelors are unmarried.
No one who believes that God exists is an
It is important to see that the truth of a
necessary truth does not depend on what
the facts of the world are like. They are
always true no matter what.
Necessary Truths and the
A Priori = prior to experience or
independent of any experience of facts or
states of affairs in the world.
Necessary truths are often said to be true
a priori, true independent of any particular
Necessary Truths and
A Priori Truths
It is also said that the proof (or
justification) of a necessary truth does not
depend on any particular facts of the
Empirical (or Contingent) Truths
Empirical = having to do with experience
Contingent = depending on experience
A statement expressing an empirical truth
is true in virtue of the facts. An empirical
statement is empirical because its truth
value (whether it is true or false) depends
on what the world is like.
Empirical (or Contingent) Truths
Empirical Statement: Microorganisms live
Empirical truth: Over 6 billion people live
Empirical falsehood: Germany won WWII.
Empirical Truths and
A Posteriori Truths
A posteriori = with experience or
depending on experience of the facts
Empirical truths are sometimes called a
posteriori truths because empirical truths
depend on what the facts are like, and
facts are known through some kind of
Necessary and Empirical Truths
Empirical (or contingent) Truths
Rationalism and Empiricism
Now we can begin explaining the
rationalist and empiricist approaches to
knowledge. We will also mention
skepticism, because it is a problem that
the rationalists and empiricists have to
What can we know and how much do we know?
To help answer these questions, we need a
theory of epistemic justification. Knowledge is
justified true belief. If we can determine when
and how our beliefs are justified, then we can
determine the scope and limits of our
knowledge. In broad strokes, there are three
main theories about epistemic justification:
Skepticism says that there is no adequate
justification for our beliefs, so we can never attain
knowledge. We can have true beliefs, but no
Global Skepticism denies that there can be
knowledge of any kind about any subject matter.
Not many people hold global skepticism, but it is
hard to defeat in conversation
Local Skepticism denies that we can have
knowledge regarding some subject matters, but not
all, or that some methods of justification are not
reliable (like reading fortune cookies, astrology,
psychic hotlines, alternative medicine, or TV news).
An empiricist holds that our beliefs can be best
justified in light of the evidence we receive from
our senses. We therefore can know something if
we can justify it with respect to what we see,
hear, and feel about the world. According to
empiricism, natural sciences like physics,
chemistry, and biology produce the most reliable
knowledge. We can know something if we can
justify it through what we can experience
through our senses.
Criticism of rationalism
Necessary truths are just tautologies (true by
definition or true analytically or true in virtue of
logical form) and don’t say much about the
Rationalists produce absurd metaphysical
claims about reality because they go too far
and end up making bogus a priori claims that
are also synthetic in order to say something
meaningful about the world.
John Locke (1632-1704)
Bishop Berkeley (1685-1753)
David Hume (1711-1776)
John Stuart Mill (1806-1873)
Bertrand Russell (1872-1970)
Logical Positivists: A.J. Ayer (1910-1989)
William James (1842-1910)
A rationalist believes that our beliefs can
be best justified in light of rational
evidence, not sensory evidence. We can
know something if it appears true in the
light of reason, not our senses. According
to rationalism, mathematics and logic
provide the most reliable knowledge.
Plato could be called a rationalist
Rene Descartes (1556-1650)
Baruch Spinoza (1632-1677)
Gottfried Leibniz (1646-1716)
Empiricists believe that knowledge is
acquired through sense experience.
So there has to be some theory of
perception that connects sense
experience with reality:
Whenever I perceive that object S has
property P, S really has P.
3 Theories of Perception
Empiricism: Naïve Realism
Naïve Realism: What you see is what you
get. When I perceive that object S has
property P, S really has property P.
Objection to Naïve Realism
It is not always the case that what I see is the
truth. There is a difference between appearance
and reality, and sometimes appearances are
Illusions and mirages
People’s experiences differ: a wind may feel cold to
me but warm to you. Who is correct?
The buckets-of-water example: Rest one hand in
freezing water and one in hot water. Take both hands
out and put them into a bucket of warm water. The
water in the bucket will feel hot to the cold hand and
cold to the hot hand. Which hand is giving the correct
Representationalism: Our ideas (which
come from sense experience) are
representations of the external world.
There is a difference between appearance
and reality, and we do not directly
experience reality. We only directly
perceive our sense impressions. Some of
what we experience is in reality.
John Locke: Theory of knowledge
We are born with minds that are like blank
slates. There are no innate ideas. The view that
there are innate ideas is dangerous and can be
used to control people.
There are two sources of ideas: (1) sensation
(sense experience of sense objects) and (2)
The ideas of reflection are produced from the
mind’s working on the ideas of sensation:
perceiving, doubting, thinking, believing,
reasoning, knowing, willing.
Locke: Knowledge and
There are two kinds of ideas: (1) simple
and (2) complex.
Simple ideas are those like the idea of the
color yellow (from sensation) or the idea of
pain (from reflection) that cannot be
broken down into other ideas.
Complex ideas are made up of simple
ideas. The mind can put simple ideas
together to make a complex idea, like the
idea of a golden mountain.
Locke: Knowledge and
The mind creates complex ideas. The
(1) joins ideas
(2) brings them together to compare them
(3) abstracts (abstract the idea of “man”
from my experiences of John and Harry.)
Representationalism: Primary and
There are two kinds of qualities. A quality is the
power in an object to produce any idea in my
Primary qualities are those that really do exist in
the bodies themselves. These include: Shape,
Solidity, Extension, Motion or Rest, Number
Secondary qualities are those that do not really
exist in the bodies themselves. These include:
Tastes, Colors, Sounds, Odors, and certain
Feelings of Touch, like softness or roughness.
Qualities do not just float around. They
have to be in something. Something has to
hold them together and organize them.
The power to produce ideas in my mind
has to be in something. This something is
substance, which Locke takes to be
Substance is matter, but we cannot say
what it is because we never perceive it.
A Problem with
How can we ever know if our ideas really
represent an external reality? If all I ever
directly perceive (in my mind) are the
ideas, and not the external objects
themselves, then how can I ever know for
sure what that external reality is like at all?
How can I ever know that an external
reality exists at all?
Berkeley argues that if we are true
empiricists, then we have to reject Locke’s
idea of substance, or matter, because it is
never perceived. Matter is a meaningless
Berkeley argues that there is no mindindependent substance. The existence of
anything depends on a perceiving mind.
“Esse Est Percipi” – To be is to be
perceived (by a mind).
Rejects Locke’s distinction between primary and
secondary qualities. There are no mindindependent qualities, no-primary qualities.
Every quality is like a secondary quality. Every
quality is experienced through a perceiving
mind. Only sensed qualities are real.
“In truth, the object and the sensation are the
same thing, and cannot therefore be abstracted
from each other.”
Locke had removed beauty (and other
secondary qualities) from the world. This made
the world ugly.
If the object is the same thing as the
sensation, then this beings up the problem
that we return to a kind of naïve realism.
What we see is what we get. There seems
to be no basis for the distinction between
appearance and reality. Our ideas do not
represent an external mind-independent
world that we can be mistaken about.
Another problem is that it seems that for
anything to exist, it has to be perceived by
a mind. But if a tree falls in the woods and
no one is there to hear it, does it make a
If we all close our eyes, does the world
So What is the cause of our ideas if not
the power in some mind-independent
material substance to produce ideas in our
minds? What keeps our ideas together?
God is the source of our ideas. God is the
mind that perceives all things. God is the
(spiritual) substance behind all things.
God sees the tree fall, so it does make a
Berkeley finds room for non-physical
spiritual beings and rejects Locke’s
materialism which seems to lead to
The abstract ideas of scientists, like the ideas of
force, attraction, and gravity, do not refer to
anything real. Only sensed qualities exist. There
is nothing other than what we can perceive. But
these ideas are still useful ideas that can help us
explain things. They just do not refer to anything
There is no causality. We never see that. Things
just follow each other in time: A follows B, but it
is never possible to say that A is the cause of B.
God orders the behavior of all things.
Explaining a similar empiricist view, Hume
distinguished between (1) impressions and
Every idea comes from some impression
from sense experience.
If a term has any meaning, then it must be
connected to an idea derived from some
sense impression. If it is not, then the term
Hume: Empiricism and Skepticism
Hume thinks that if we are strict empiricists, then
it is going to be very hard or impossible to
answer these questions:
Is there an external world?
Can induction really work?
Can we ever know the ultimate substance?
Is there a self?
Is there causality (as necessary connection)?
Is there a God?