1. LECTURE 20 THE PRINCIPLE OF SUFFICIENT REASON: CAN IT BE SAVED?

2. 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.

3. 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)

4. 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.

5. (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)!

6. 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 S c.

7. S c MUST NECESSARILY IMPLY BIG C ACCORDING TO (PSR) S c MUST BE A SUFFICIENT EXPLANATION OF BIG C. SO IT MUST EXPLAIN EVERY PART OF IT. IT CANNOT BE A PARTIAL EXPLANATION. S c BIG C NECESSARY IMPLICATION

8. BUT S c CANNOT BE CONTINGENT! IF S c WERE CONTINGENT, THEN IT WOULD BE PART OF BIG C !! BUT AN EXPLANATION CANNOT EXPLAIN ITSELF (EXPLANATIONS CANNOT BE CIRCULAR). SO S c 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).

9. 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)

10. 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?