Philosophy 1110 (Introduction to Philosophy) Yalçin

Handout on the Incompatibilist Argument against Free Will

Master argument:

(1) Either Determinism is true, or indeterminism is true (1) D or I

(2) If Determinism is true, then there is no free action (free will) (2) D C ¬F

(3) If Indeterminism is true, then there is no free action (free will) (3) I C ¬F

\ (4) There is no free action (free will) \ (4) ¬F

Argument in support of premise (2) of the master argument:

(1) Every thing (event) has a sufficient cause. {Determinism, assumed for conditional proof}

(2) For any action A that X performs, there is a set of conditions, C (internal and external conditions, including the laws of the universe), such that C is the sufficient cause of X’s performing A. {from 1, by universal instantiation, and some elaboration}

(3) Take some particular action, a, such that X performs a in the actual world; there is a set of conditions, c (internal and external conditions, including the laws of the universe), such that c is the sufficient cause of X’s performing a. {from 2, by universal instantiation}

(4) In any other possible world in which c is present, X performs a. {from 3, by the definition of sufficient cause}

(5) Given c, X cannot refrain from doing a. {from 4}

(6) If X performed a freely in c, then X could have refrained from doing a in c. {from the definition of free action}

(7) X did not perform a freely in c. {from 4 and 5 by MT}

(8) Take any any action A, and any sufficient cause C of that action: X did not perform A freely in C. {generalizing from 7, given the fact that a and c were arbitrarily chosen }

(9) No action of X’s is freely performed {from 8}

(10) If every thing has a sufficient cause, then no action of X’s is freely performed {from 1 and 9, eliminating our dependence on the assumption in (1)}

Form: Conditional Proof

(1) Assume D

:

:

:

(9) Prove ¬F on the basis of the assumption in (1)

\ (10) If D, then ¬F

Justification: if assuming D leads to ¬F, then we can express this with an "if-then".