Transcript RATIONALISM – CARTESIAN MOTIVATIONS

Classical Empiricism
• The fundamental source of knowledge is sensory
experience.
• Knowledge can be of both necessary and contingent
truths. Necessary truths are still the more interesting as
they tell us about the essential properties of things.
• There are no innate ideas.
• Our senses are fallible, limited and subjective. But reason
is also fallible and limited.
• We cannot learn about the world by turning away from it.
We need to investigate it empirically – scientifically.
• A priori knowledge of substantial truths is impossible.
Only a priori knowledge of analytic truths is possible.
• Necessary truths are knowable a priori but only because
they are trivial truths of definition.
EMPIRICISM – MOTIVATIONS
Rationalists are
“spiders”: they
spin complex
metaphysical
systems out of
their entrails.
Empiricists are
“bees”: they gather
“pollen” (data) and
works it into “honey”
(knowledge).
Francis Bacon (1561-1626)
The book of
nature is
written in the
language of
mathematics.
Nature is to be
probed by
observation and
experimentation:
science.
Galileo Galilei (1564-1642)
There are no
innate ideas.
John Locke (1632-1704)
Knowledge is
the agreement of
ideas that
originate in
experience.
Pioneering use of
telescope led to
discoveries that
undermined
Aristotle’s view of
the heavens.
EMPIRICISM – LOCKEAN MOTIVATIONS
There are no
innate ideas.
What’s
the proof?
How could you
know necessary
truths such a
“nothing can be
both black and
white” without
experience of these
colours?
John Locke (1632-1704)
If there were innate
ideas/principles,
they’d be
“universally
assented” to.
There are no moral
rules common to
every society.
But even if there were
things we all agreed on,
this wouldn’t show they
were innate. They could
arise from common
types of experience.
“Children, idiots
and savages” are
unaware of
concepts such as
God and cause.
E.g. we all learn
the ideas of red
and object and
sky because we
all experience
these things.
All ideas are either
come from sensation or
reflection. The simple
ideas of sensation are
the fundamental ideas.
LEIBNIZ’S REACTION TO LOCKE
Our ideas are
innate but not
actually
present in the
mind.
A mind is not
a tabula
rasa. It is like
a block of
marble.
The marble has
veins running
through it that
define a statue of
Hercules.
Gottfried Leibniz (1646-1716)
In the same way, our
ideas are potentially in
our minds but we need
the right experiences to
activate them
By hitting the
marble at its
veins, the
embedded statue
becomes
exposed.
EMPIRICISM – LOCKE AND NECESSARY TRUTHS
We can’t learn that
all triangles have
internal angles that
sum to 180o
through experience
– we can’t check all
of them.
But how do
we account
for
knowledge
of necessary
truths?
We learn the
ideas of triangle,
angle, degree
and so forth from
experience.
…and you can’t say: as
all triangles have property
X so it is necessary
property without having
experienced all
triangles…
You can’t say: all
triangles have this
property so it is
necessary without
having the idea of
necessity…
It presupposes we have
the idea of necessity.
How do we learn this
from experience?
…and you can’t say: well, my idea of
a triangle shows it to have property
X on the basis of what I have seen
so far, because that’s no proof it is
necessary – for all we know, all the
triangles you’ve seen so far might
have been green.
How does our mind
succeed in representing
just the necessary
features?
But this doesn’t solve
the problem.
Once we have
these ideas,
we can
consider their
relations to one
another in our
mind.
We can observe that it
follows from the idea of a
triangle and the idea of an
angle and the idea of 180
that a triangle must have
internal angles that sum
to 180o
So, we learn
necessary truths
by examining our
ideas and the
relationships
between them.
EMPIRICISM – HUMEAN MOTIVATIONS
All knowledge
begins with
impressions: the
deliverances of
the senses.
Hume’s Copy
Principle:
Our mind
makes ideas:
faint copies of
impressions
that enable us
to think off-line.
“All our simple
ideas in their first
appearance are
derived from simple
impressions, which
are correspondent
to them, and which
they exactly
represent”
David Hume ((1711-1776)
Proof?
Impressions ‘enter
with the most force
and violence’ or
are more
‘vivacious’ than
ideas
People lacking either a
sensory modality (e.g. taste)
or impressions (e.g. tastes of
wine) cannot form ideas of
these things.
Find me an idea
that does not
originate in
experience.
EMPIRICISM – HUMEAN MOTIVATIONS
What about
necessary
truths? And
metaphysical
concepts of God
and cause and
self?
The books of
metaphysics
should be
“consigned to
the flames”
There are no
substantial
(interesting,
metaphysical) a
priori knowable
truths.
Relation of ideas = analytic and
necessary truth.
“All bachelors are unmarried”
Hume’s Fork:
Any truth is either a
“relation of ideas”
or “a matter of fact”
The idea of unmarried is
analytically part of the idea of a
bachelor.
But what about important
metaphysical truths such as “God
exists”? “Every event has a
cause”?
Matter of fact = synthetic and
contingent truth.
“Bernard is a bachelor”
The idea of being a bachelor is no
part of the idea of Bernard. It’s
just a fact about Bernard that he
is a bachelor.
Either they are mere truths of
definition or they are, if true, only
contingently so.
HUME AND CAUSATION
Rationalists say
that the concept
of cause is an
innate concept
and that we live
in a world where
nothing happens
without a cause.
What’s a
necessary
connexion?
How can
experience
discover this?
The concept of
cause is
learned from
experience.
What’s a
necessary
connexion?
How can
experience
discover this?
We get the idea of a
necessary connexion
from seeing X-then-Y
many times.
X causes Y =
(i) X and Y are
spatiotemporally
contiguous.
(ii) X comes before Y
(iii) There is a
necessary connexion
between cause and
effect.
So, causation boils down to the expectation
that Y will follow X.
So, what does it mean
to say that one thing
causes another?
So reason cannot
discover causal
connections.
Furthermore, there’s no
real relation of causation
out there in the world.
Causation is a
psychological relation
between
impressions/ideas.
Suppose that a brick is
thrown at a window
and it breaks. We say
that the thrown brick
caused the broken
window.
But does it follow
logically from the
description of the first
event – the thrown
brick – that the second
event – the broken
window – would
follow?
No!
LOGICAL POSITIVISM
The Logical
Positivists were
20th century
Empiricists.
Second, some clearly
meaningful truths aren’t
verifiable because they are
general. For example, “all
badgers are mammals” is not
verifiable because we can’t
check all of them. But if we
find that many badgers are
mammals, that is good
evidence that all of them are.
First, we can’t verify
whether “there are
badgers on Pluto” with
our senses as we
can’t get there. But in
principle we can.
As Hume said,
every truth is
either an
analytic truth or
a synthetic
truth.
So, we must
make it:
The analytic truths
included not just trivial
definitions but also
mathematical and
logical truths.
A sentence is
meaningful if it can be
verified in principle
(falsified) by the
senses or if the
evidence of the
senses raise make it
highly probable that it
is true.
So, “old-fashioned” metaphysical claims such
as “God exists” or “Every event has a cause”
are either meaningless or contingent claims
that can be scientifically verified.
But this can’t be quite
right, as the Logical
Positivists knew.
The synthetic truths
are the ordinary truths
and the scientific
truths.
At the heart of Logical
Positivism is the
Verification Principle:
A sentence is meaningful
if it can be verified
(falsified) by the senses.
LOGICAL POSITIVISM - PROBLEMS
The principle is
meaningless by its own
standards: we cannot
verify with the senses
whether it is true.
Swinburne’s Toy
Cupboard: we can
make sense of
unverifiable
situations.
Won’t the religious
experiences of many
people lend support
to the claim that
“God exists”.
We believe in atoms even though
we can’t seem because we have
good theoretical evidence that they
exists. Can’t we argue in the same
way that God exists because he is
the best theoretical explanation of
the universe around us?
The verification
principle, even
when weakened, is
flawed.
Hick: the claim “there is an
afterlife” passes the
verification test. We will
just have to wait until we
die to verify it.
Positivists claim that
analytic sentences
express necessary truths
(such as the truths of
maths) . But there is no
analytic/synthetic
distinction according to
Quine.
Quine and the Analytic/Synthetic Distinction
Analytic sentences are
sentences true in virtue
of their meaning.
E.g. “all metals
conduct
electricity”
Synthetic truths are
sentences true in virtue
of how the world is.
E.g. “it is sunny
today”
Instead, we
should think of our
knowledge as
forming a web.
So there is no sharp
analytic/synthetic
distinction.
So what was once held
true and analytic (e.g.
“water is an element) can
turn out to be synthetic
and false.
At the centre are beliefs
that are least susceptible to
rejection / revision – e.g.
mathematical, logical
beliefs. Perhaps these can’t
be rejected.
A bit further out are basic scientific
beliefs. Rejecting these would
cause us to have to revise much of
what we believe: e.g. “badgers are
animals”, “the earth is round”.
But history shows that we
often make mistakes. We
might make discoveries that
will require us to revise our
definition of a metal as
something that conducts
electricity.
By making this
distinction, the
positivist can
have his cake
and eat it.
Further out, we
have beliefs that
could be
rejected/revised
with less
trouble: e.g. “I
left my keys at
home on the
kitchen table
this morning.”
They can allow
necessary truths
as simply
expressing
relations
between
concepts (rather
like Locke had
suggested).
But how do we
discover these
truths? The
Positivist must
say, “ through
reason” as she is
an Empiricist
But we can’t have checked all
bits of metal. So, we must be
making the following decision:
we have evidence enough to
think that all metals conduct
electricity and so we’ll make it
part of the definition that it does.