Test 3
Review
The Question
•  What am I?
–  What sort of thing am I?
•  Am I a mind that “occupies” a body?
•  Are mind and matter different (sorts of)
things?
Descartes’ Answer
•  What I am is an immaterial soul that
“occupies” a material body.
•  Descartes is a “Substance Dualist” who
believes that mind and matter are two
irreducibly different kinds of basic “stuff.”
–  Descartes believes that mental states are not
identical to brain states.
Descartes
•  I can conceive of myself without a body,
–  As a disembodied mind.
•  I cannot conceive of myself without a mind,
–  As a mindless zombie.
•  So, having/being a mind is an essential
property, while
•  Having a body is merely an accidental
property.
Life After Death?
•  If there is such a thing as life after death, then there
must be a “part” of you that continues to exist after
the death of your body.
•  So, if you believe in life after death, you are already
committed to the idea that you are something distinct
from your body …
–  i.e., distinct from any material object.
•  So, materialists of all varieties must deny the possibility of life after
death.
Descartes
•  A Dualist
–  Descartes thinks that what I am is a mind, and that
I occupy a material body.
•  “Thinking” (being conscious) is an essential property.
•  “Being extended” (occupying space—having a body) is
merely an accidental property.
–  So, there are two fundamental and distinct basic
kinds of stuff: mind and matter.
Mind/Body (or Substance) Dualism:
There are two distinct, fundamental and irreducible,
sorts of things in the world…
MINDS
•  Conscious Beings:
–  Non-material beings which
are the subjects of conscious
experience.
•  Descartes:
–  Res cogitans
–  “Thinking” but non-extended
beings (beings that do not
occupy space).
BODIES (Matter)
•  Material Beings:
–  Material (“corporeal”) beings
that cannot be the subjects of
conscious experience.
•  Descartes:
–  Res extensa
–  Extended beings (beings that
occupy space), but are not
capable of “thinking.”
How many kinds of “stuff?”
Monism:
Dualism:
Minds and
Matter
Materialism: Everything is
material
Idealism:
Everything
is mental
Des
and cartes
Lock
e
Eliminative
Materialism
Berkel
ey
There are
no
mental
states,
just like
there are
no
ghosts.
Identity
Theory
Mental
states are
identical
to brain
states, just
like water
is
identical
to H2O.
Epiphenomenalism
Mental states (qualia) are real
but causally inert.
Jackson
Descartes’ Arguments for Dualism
•  Bodies are divisible. Minds are not. So they
cannot be the same thing.
•  “Mind” and “Matter” are conceptually distinct
—the concept of each is independent of the
concept of the other. So, it is possible for one
to exist without the other. So, they must be
different.
A Problem: Causal Interaction
•  On Descartes’ view (dualism), minds and
bodies are fundamentally distinct kinds of
things, distinct kinds of “substance.”
•  And yet, he believes they causally interact
with one another.
–  Exp.: Sense perception, willful action.
•  But it seems impossible to explain how
things with nothing in common could
“influence” each other.
Carruthers: Mental States are Identical
to Brain States
•  Carruthers turns this problem for dualism into
an argument against it (an argument for “the
identity” theory).
–  1) Only physical events can cause physical events;
–  2) Yet thoughts (mental states) can cause physical
events (willful action);
–  3) So thoughts (and other mental states) must be
(must be “identical to”) physical events.
Materialism
•  The identity theory:
–  1) Everything that
exists is composed of
matter,
–  2) Mental states
exist, but are identical
to physical states
(brain states), in the
way that water is
identical to H2O.
•  Eliminative
Materialism:
–  1) Everything that
exists is composed of
matter,
–  2) Mental states do
not exist. Like
ghosts, we once
believed they existed,
but now we know
otherwise.
How many kinds of “stuff?”
Monism:
Dualism:
Minds and
Matter
Materialism: Everything is
material
Idealism:
Everything
is mental
Des
and cartes
Lock
e
Eliminative
Materialism
Berkel
ey
There are
no
mental
states,
just like
there are
no
ghosts.
Identity
Theory
Mental
states are
identical
to brain
states, just
like water
is
identical
to H2O.
Epiphenomenalism
Mental states (qualia) are real
but causally inert.
Jackson
The Identity Theory
•  Rejects Dualism: a variety of Materialism.
•  Claims that everything that exists is, ultimately,
material.
•  Unlike Eliminative Materialism, accepts that
mental states are, in some sense, “real.”
•  But claims that what they really are are states of
the brain and/or central nervous system.
–  So thoughts (and other “mental states”) are identical
to brain states in just the way that water is identical
to H2O.
Carruthers and Leibniz’ Law
•  Carruthers argues that mental states are
identical to brain states: dualists disagree.
•  So, the debate concerns whether or not these
things are identical.
•  Leibniz’ Law states a general truth about
identical things: if two things are identical,
they have the same properties.
–  So if things have different properties, they
cannot be identical.
Carruthers’ Rebuttals
•  Objection: The Argument from Certainty
–  I can be certain of mental states, but not brain
states.
–  C: “being such that I can be certain about it” is
not a property that things have.
•  Objection: The Argument from Color
–  I can have green after-images, but brain states
can’t be green.
–  C: After-images aren’t actually green.
Jackson
•  A “Qualia Freak”
–  Qualia: What it’s like to smell a rose, etc.
•  There are “truths” about what it is like to smell
a rose, etc.
•  These are not “truths” of physics.
•  So, there are truths that are not truths of
physics.
Jackson’s Dilemma
•  Jackson recognizes there are truths about what
it is like to smell a rose;
•  And believes that these truths are not truths of
physics.
•  Dilemma: Doesn’t claiming there are truths
that are not truths of physics force one into
dualism? Doesn’t this force one to reject
materialism?
Jackson’s Solution
•  Distinguish (mere) “Materialism” from (what
he calls) “Physicalism.”
–  Materialism: Everything that exists is material.
–  Physicalism: Materialism plus the claim that all
truths are truths of physics.
•  Jackson is forced to reject physicalism.
•  But accepting materialism while rejecting
physicalism leaves him with
Epiphenomenalism.
Materialism
Physicalism
•  Everything that
exists is composed
of matter.
•  Everything can, in
principle, be fully
explained in terms
of the laws of
physics.
Epiphenomenalism
•  Everything that exists is composed of
matter.
•  Not everything can, even in
principle, be explained in terms of
the laws of physics.
–  Qualia exist, but cannot be explained in
terms of the laws of physics. They are
caused by physical events, but do not
themselves cause anything. Events in
the physical world would be no different
without them.
How many kinds of “stuff?”
Monism:
Dualism:
Minds and
Matter
Materialism: Everything is
material
Idealism:
Everything
is mental
Des
and cartes
Lock
e
Eliminative
Materialism
Berkel
ey
There are
no
mental
states,
just like
there are
no
ghosts.
Identity
Theory
Mental
states are
identical
to brain
states, just
like water
is
identical
to H2O.
Epiphenomenalism
Mental states (qualia) are real
but causally inert.
Jackson
Epiphenomenalism
•  What you get if you accept qualia (truths
about what experience is like) while rejecting
dualism.
•  Qualia are real, but causally impotent: they are
caused by physical events, but cannot
themselves cause physical events.
•  So, the world wouldn’t be any different if we
were all “zombies.”
–  Consciousness is “real” but doesn’t do anything.
Why can’t qualia cause?
•  According to science, all causes are physical, and so
must be describable in the terms of physics.
•  But qualia, Jackson has argued, cannot be described
in the terms of physics.
–  (Facts about them are not facts of physics.)
•  So, qualia cannot be the causes of physical events.
•  Epiphenomenalism is the view that qualia real, but
causally impotent.
Mental States and Causality
The Turing Test
•  How could we tell whether or not a computer
could “think?” How could we tell if it was
“conscious?”
•  Turing proposes a “test,” and says if a
computer could pass it, we would have to say
that it thinks.
–  The test involves answering questions in a way
that could “fool” us into believing we were talking
to a human being.
The Issue
•  Turing’s discussion of the “Objection from
Consciousness” helps us understand the core of the
issue.
•  We cannot see “inside” other people’s minds, and yet
we believe they are conscious.
–  So, we must believe this because of how they “behave”—
specifically, how they “talk.”
–  If a computer behaves in the same way, we must either
admit that it thinks or deny that other people think, because
we use the same “test” in both cases.
The Turing Test
•  Turing believes that if a computer can produce “language” we
cannot distinguish from that produced by a human being, then it
thinks.
•  The key point is that we have no direct access to the consciousness
of other human beings, and so no direct knowledge of whether or
not other human being think.
•  So, apparently we infer that something thinks by observing its
behavior, and the only behavior that is relevant is the use
language.
•  So if computers can produce language we cannot distinguish from
that of human beings, we must either deny that either of them
thinks (which amounts solipsism), or we must admit that both do.
The point is that the evidence is the same in both cases.
I Think: Do You?
Turing’s Conclusion:
•  The criteria we in fact use to attribute thinking
(consciousness) to other human beings are behavioral.
–  These criteria concern linguistic behavior—how a think talks, not what
it looks like.
•  If these are the criteria I use with other human beings, it would
be inconsistent to demand some “higher standard” of
computers.
•  So, if a computer could meet the same standards of linguistic
behavior as do other human beings (i.e., if it could
successfully play the imitation game), we must, on pain of
inconsistency, claim that it “thinks,” i.e., that it is “conscious.”
Good Luck!
Think
before you answer!