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| Introduction to Philosophy | Notes | This is not a substitute for coming to class - or for reading the material. | Richard Lee |
| Philosophy 2003 | Copyright © 2007, Richard Lee | Spring 2007 | |
Proof by reductio ad absurdum
1. Assume there is no necessary thing.
2. Then all things are contingent. (from 1 by definition)
3. "Anything which is capable of not existing at some time or other does not exist." (IP3 168a)
4. "If therefore all things are capable of not existing, [then] there was a time when nothing existed in the Universe." (IP3 168a)
5. "But if this is true, [then] there would also be nothing in existence now . . ." (IP3 168a) ("ex nihil nihil fit")
6. There is something in existence now. (obvious)
7. So, Contradiction: there is nothing in existence but something is in existence.
8. So, there is a necessary thing. (by reductio)
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