LECTURE 25
DESCARTES’S
ARGUMENT AND A
LEIBNIZIAN
ARGUEMENT
DESCARTES’S ARGUMENT AGAINST
PHYSICALISM (FOR DUALISM)
ARGUMENTS FOR DUALISM
“DESCARTES’ ARGUMENT”
I CAN CONCEIVE OF THERE BEING
NO PHYSICAL BODIES.
I CANNOT CONCEIVE THAT I DO
NOT EXIST.
THEREFORE:
I AM NOT A PHYSICAL BODY.
A LOGICAL PRINCIPLE
THE INDISCERNIBILITY OF IDENTICALS
OR BETTER: THE
DISTINCTNESS OF
DISCERNIBLES
(DD) FOR ANY PROPERTY F AND ANY
THINGS X AND Y, IF X HAS F AND Y
DOES NOT, THEN X IS NOT IDENTICAL
WITH Y.
THIS PRINCIPLE DD SEEMS
UNIMPEACHABLE
IF X AND Y ARE THE VERY SAME
THING (NOT JUST SIMILAR OR
EXACTLY ALIKE), THEN ANYTHING
THAT IS TRUE OF X IS TRUE OF Y
(THAT IS, X).
IN LOGICAL SYSTEMS IT USUALLY IS
CALLED “THE SUBSITUTIVITY OF
IDENTICALS.”
NEVERTHELESS, THERE SEEMS TO BE
SOMETHING WRONG WITH THE
ARGUMENT
• COMPARE:
• (1) I CAN CONCEIVE OF BATMAN NOT
EXISTING AND AT THE SAME TIME BRUCE
WAYNE EXISTING.
• (2) I CANNOT CONCEIVE OF BRUCE WAYNE
EXISTING AND AT THE SAME TIME BRUCE
WAYNE NOT EXISTING.
THEREFORE:
(3) SO BATMAN HAS A PROPERTY THAT
BRUCE WAYNE DOES NOT.
THEREFORE (BY DD)
(4) BATMAN IS NOT BRUCE WAYNE.
???!!!
VAN INWAGEN’S DIAGNOSIS
ACCORDING TO VAN INWAGEN,
THE PROBLEM IS THAT THE
PHRASE”
“…CAN BE CONCEIVED BY ME NOT
TO EXIST”
DOES NOT EXPRESS (DENOTE,
DESIGNATE) A PROPERTY.
A TEST FOR EXPRESSING A PROPERTY
CONSIDER A SENTENCE CONTAINING A PROPER
NAME (OR OTHER DESIGNATOR OF AN
INDIVIDUAL) AND REPLACE THE NAME BY THE
VARIABLE ‘X’.
“OBAMA IS PRESIDENT”
“X IS PRESIDENT”
“ANDERSON IS A PHILOSOPHER”
“X IS A PHILOSOPHER”
CALL THE RESULTING EXPRESSION A
“LOGICAL PREDICATE”
THE TEST: A LOGICAL PREDICATE EXPRESSES
(DENOTES, SIGNIFIES, CORRESPONDS TO) A
PROPERTY ONLY IF THE RESULTS OF
REPLACING ‘X’ BY TWO DIFFERENT
DESIGNATIONS OF THE SAME INDIVIDUAL ARE
BOTH TRUE OR BOTH FALSE.
TRY:
“COMMISIONER GORDON KNOWS THAT X IS
BATMAN.”
THE LOGICAL PREDICATE IN
DESCARTES’ ARGUMENT
“X CAN BE CONCEIVED BY ME NOT TO EXIST”
CONSIDER THE TWO DESIGNATORS:
“THE INSTRUCTOR OF PHIL 100E (S 2014)”
“I”
BOTH OF THESE DESIGNATE ME. BUT THE
LOGICAL PREDICATE FAILS THE TEST. (WHY? A
VERY INTERESTING QUESTION. CF.
PHILOSOPHY OF LANGUAGE).
SOME PREDICATES INVOLVE
CONCEPTS OF THINGS
HERE IS ONE POSSIBLE EXPLANATION OF WHY
THE DIFFERENCE OF DISCERNIBLES CANNOT BE
APPLIED TO CERTAIN PREDICATES: THE
PREDICATE AREN’T SIMPLY ABOUT A THING, BUT
ARE ALSO SENSITIVE TO THE CONCEPT
INVOLVED. CONSIDER:
“JONES BELIEVES THAT THE BANK
ROBBER IS A CROOK.” (TRUE)
SUPPOSE THE BANK ROBBER WAS
DISGUISED AND WAS IN FACT THE
PRESIDENT OF THE BANK
“JONES BELIEVES THAT X IS A CROOK” IS A
LOGICAL PREDICATE BUT SUBSTITUTING A
DESIGNATING TERM IN FOR “X” MAY GIVE A
DIFFERENT RESULT DEPENDING ON THE
CONCEPT IT EXPRESSES:
“JONES BELIEVES THAT THE BANK PRESIDENT IS
A CROOK” (FALSE)
SUCH CONTEXTS ARE CALLED
“INTENSIONAL CONTEXTS”
MANY PSYCHOLOGICAL VERBS GIVE RISE TO
SUCH CONTEXTS (CONTEXTS WHERE THE
SUBSTITUTION TEST FAILS):
BELIEVES, KNOWS, WONDERS WHETHER,
DESIRES, SPECULATES, CONJECTURES, TRIES,… .
ALSO MODAL NOTIONS: NECESSARILY, POSSIBLY,
IT IS IMPOSSIBLE THAT, IT IS CONTINGENT THAT,
ENTAILS,…. .
IT IS FAIR TO SAY THAT THE RESULTING
LOGICAL PREDICATES DO NOT SIMPLY
EXPRESS PROPERTIES
“COMMISIONER GORDON KNOWS THAT X IS
BATMAN” DOES NOT SIMPLY EXPRESS A
PROPERTY OF WHATEVER IS DESIGNATED BY
THE TERM PUT IN FOR “X”. “BATMAN” AND
“BRUCE WAYNE” GIVE DIFFERENT RESULTS.
THIS LOGICAL PREDICATE EXPRESSES A
PROPERTY OF A THING CONCEIVED IN A
CERTAIN WAY.
BACK TO DESCARTES’S ARGUMENT
I PERHAPS CANNOT CONCEIVE OF MYSELF OF AS
NOT PRESENTLY EXISTING. I CAN CONCEIVE OF
MY BODY AS NOT PRESENTLY EXISTING. BUT
“MYSELF” AND “MY BODY” MAY BOTH
DESIGNATE ME – CONCEIVED IN DIFFERENT
WAYS.
WHATEVER THE EXACT EXPLANATION OF THE
LOGICAL ERROR, THE ARGUMENT DOES NOT
SEEM TO BE VALID.
GOTTFRIED WILHELM VON LEIBNIZ
A LEIBNIZIAN ARGUMENT AGAINST
PHYSICALISM
(1) IT IS IMPOSSIBLE THAT PHYSICAL THINGS
SHOULD BE CAPABLE OF THOUGHT AND
PERCEPTION.
(2) I AM CAPABLE OF THOUGHT AND
PERCEPTION.
THEREFORE:
(3) I AM NOT A PHYSICAL THING
IT SEEMS IMPOSSIBLE TO IMAGINE
HOW THOUGHT AND PERCEPTION
COULD BE PRODUCED BY SOMETHING
PHYSICAL
• LEIBNIZ’S THOUGHT EXPERIMENT (QUOTE P.
219)
IF ONE WERE SMALL ENOUGH TO PASS INTO
SOMEONE’S BRAIN, ONE WOULD FIND NO
PHYSICAL MECHANISM PRODUCING THOUGHT
OR PERCEPTION.
THERE IS NO DOUBT THAT THINKING
AND PERCEIVING ARE MYSTERIOUS
PHYSICS, CHEMISTRY AND BIOLOGY HAVE
OFFERED NO PLAUSIBLE EXPLANATION OF THE
EXISTENCE OR NATURE OF THOUGHT AND
PERCEPTION. EVOLUTION DOES NOT SEEM TO
HELP EXPLAIN THE DEVELOPMENT OF
CONSCIOUSNESS AND RATIONAL THOUGHT. IF
THE BRAIN PRODUCES THE RIGHT BEHAVIOR,
SURVIVAL IS ENHANCED – BUT THERE IS NO
APPARENT NEED FOR CONSCIOUSNESS.
BUT DOES LEIBNIZ’S THOUGHT
EXPERIMENT FAVOR DUALISM?
VAN INWAGEN ARGUES THAT, ALTHOUGH
THOUGHT AND PERCEPTION ARE MYSTERIOUS,
DUALISM HAS NO ADVANTAGE IN ATTEMPTS TO
EXPLAIN HOW SUCH THINGS OCCUR.
SUPPOSE THAT THESE THINGS ARE CAUSED BY A
NON-PHYSICAL THING. IS IT COMPOSITE? IS IT
SIMPLE? ARE YOU ABLE TO IMAGINE HOW IT
MIGHT PRODUCE THOUGHT AND ALLOW FOR
PERCEPTUAL EXPERIENCE?
THE “OUTSIDER” WOULD SEE CERTAIN
PHYSICAL THINGS GOING ON THE
BRAIN
• THE “INSIDER”, THE ONE WHOSE BRAIN IS
PRODUCING THOUGHT OR EXPERIENCE,
WOULD HAVE OR EXPERIENCE THESE THINGS
DIFFERENTLY.
• BUT COULDN’T THE PHYSICAL EVENTS JUST BE
THE VERY SAME EVENTS AS THE “MENTAL”
EVENTS?
“WHERE” ARE THE MENTAL EVENTS
OCCURRING?
IN SO FAR AS EVENTS HAVE LOCATION,
THE MENTAL EVENTS ARE OCCURRING
IN THE VERY SAME PLACE AS THE
PHYSICAL BRAIN EVENTS – THEY ARE
THE PHYSICAL BRAIN EVENTS
(ACCORDING TO THE PHYSICALIST)
VAN INWAGEN CONCLUDES THAT THE
LEIBNIZIAN ARGUMENT FAILS
THE THOUGHT EXPERIMENT BRINGS
OUT HOW STRANGE MENTAL EVENTS
ARE (EXPERIENCED FROM THE
“INSIDE”), BUT IT DOES NOT SHOW
THAT PHYSICAL THINGS CANNOT HAVE
THOUGHTS OR EXPERIENCE.
G. E. MOORE
A THIRD ARGUMENT THAT A PERSON
IS NOT A BODY
• G. E. MOORE’S OBSERVATION ABOUT
“WHERE” HE IS.
(1) I AM CLOSER TO MY HANDS THAN I AM TO
MY FEET.
(2) MY BODY IS NOT CLOSER TO MY HANDS
THAN TO MY FEET.
THEREFORE (BY DD):
(3) I AM NOT MY BODY.