LECTURE 20
THE PRINCIPLE OF
SUFFICIENT REASON:
CAN IT BE SAVED?
AQUINAS’S THIRD WAY
ST. THOMAS’S “THIRD WAY”, AN ATTEMPTED
PROOF OF THE EXISTENCE OF A NECESSARY
BEING, SEEMS TO MOVE FROM THE FIRST OF
THESE TO THE SECOND:
(1) FOR EVERY CONTINGENT THING X, THERE IS A
TIME T SUCH THAT X DOES NOT EXIST AT T.
(2) THERE IS A TIME T SUCH THAT FOR EVERY
CONTINGENT BEING X, X DOES NOT EXIST AT T.
THE TWO MAIN OBJECTIONS
(1) THE OBJECTION FROM QUANTUM
MECHANICS.
(A) QUANTUM MECHANICS IS CERTAINLY
TELLING US SOMETHING TRUE ABOUT THE
WORLD. IT WOULD BE BETTER IF THERE
WERE AN UNCONTROVERSIAL
INTERPRETATION. NEVERTHELESS, THIS
OBJECTION HAS SOME FORCE AGAINST (PSR)
PROBABLISTIC EXPLANATIONS?
(B) SOME PHILOSOPHERS OF SCIENCE THINK
THE MERE FACT THAT AN EVENT HAS A
CERTAIN PROBABILITY OF OCCURING SHOULD
COUNT AS AN EXPLANATION. THIS MAY BE
O.K., BUT IT JUST GIVES UP (PSR). THIS
LATTER REQUIRES SUFFICIENT REASONS FOR
THINGS BEING TRUE.
(2) THE ARGUMENT THAT (PSR) HAS
AN ABSURD CONSEQUENCE
VAN INWAGEN’S VERSION OF THE OBJECTION
ASKED FOR AN EXPLANATION OF WHY THIS
WORLD (SAY “POSSIBLE WORLD A”) IS THE
ACTUAL WORLD. IF THERE ARE CONTINGENTLY
TRUE PROPOSITIONS, THEN THE EXPLANATION, S,
OF WHY THEY ARE ALL TRUE WOULD BE
CIRCULAR --- UNLESS IT IS A NECESSARY
PROPOSITION. BUT THEN EVERYTHING IMPLIED
BY IT IS NECESSARY! THAT’S EVERYTHING IN
POSSIBLE WORLD A (THIS WORLD)!
ANOTHER VERSION OF THE
OBJECTION
A VERY SIMILAR OBJECTION MAY BE EASIER TO
UNDERSTAND. LET ‘BIG C’ BE THE
CONTINGENTLY TRUE PROPOSITIONS ALL
TAKEN TOGETHER (THEIR CONJUNCTION). [OF
COURSE, THERE WOULDN’T BE A BIG C IF
THERE WERE NO CONTINGENT
PROPOSITIONS]. ACCORDING TO (PSR) BIG
C HAS AN EXPLANATION. CALL IT Sc .
Sc MUST NECESSARILY IMPLY BIG C
• ACCORDING TO (PSR) Sc MUST BE A
SUFFICIENT EXPLANATION OF BIG C. SO IT
MUST EXPLAIN EVERY PART OF IT. IT CANNOT
BE A PARTIAL EXPLANATION.
•
Sc
BIG C
NECESSARY IMPLICATION
BUT Sc CANNOT BE CONTINGENT!
IF Sc WERE CONTINGENT, THEN IT WOULD BE
PART OF BIG C!! BUT AN EXPLANATION
CANNOT EXPLAIN ITSELF (EXPLANATIONS
CANNOT BE CIRCULAR). SO Sc MUST BE
NECESSARY. THEN EVERYTHING IT
NECESSARILY IMPLIES IS NECESSARY - SO
BIG C CANNOT EXIST. ALL PROPOSITIONS
ARE NECESSARY! THIS IS ABSURD. WE
SHOULD REJECT (PSR).
WE DO NOT HAVE TIME TO PURSUE
THIS OBJECTION FURTHER
TENTATIVELY, THE PRINCIPLE OF SUFFICIENT
REASON SHOULD BE DOUBTED FOR THE
REASONS GIVEN. FOR THE RECORD, THERE ARE
FAIRLY PLAUSIBLE OBJECTIONS TO BOTH VAN
INWAGEN’S AND THE BIG C VERSION OF THIS
ATTEMPT TO REFUTE (PSR).
THERE ARE ALSO WEAKER VERSIONS OF (PSR) THAT
HAVE BEEN USED IN PHILOSOPHICAL
ARGUMENTS. (E.G. WILLIAM LANE CRAIG’S
KALAM COSMOLOGICAL ARGUMENT)
CAN SCIENCE TELL US WHY THERE IS
SOMETHING RATHER THAN NOTHING?
“NOTHINGNESS IS UNSTABLE”
“ONCE UPON A TIME, THERE WAS NOTHING
(WELL, EXCEPT A QUANTUM VACUUM) AND
THEN…”
A QUESTION WE HAVE NOT ASKED, BUT OF
WHICH (PSR) WOULD REQUIRE AN ANSWER IS
“WHY ARE THERE LAWS OF NATURE (AT ALL)?”
WE WILL CONSIDER SOME RELATED QUESTIONS:
WHY ARE THE LAWS SO NICE FOR LIFE?