A few weeks ago I was debating the principle of sufficient reason (PSR) with a bunch of theists and a pantheist over in the combox of Strange Notions.
To me, the PSR is blatantly false, and relatively easy to prove so. The PSR's own assumptions can show how it's self refuting. In this blog post I want to compile some of the logic I use to show what entails from the PSR's stated premises that show it's flaws. Consider this:
1. The PSR demands that everything has an explanation.
2. Explanations can only be either necessary or contingent.
3. If an explanation is contingent, it will need a further explanation that is either necessary or contingent.
4. If a necessary explanation is not an eventual option, then the only possible explanations will have to be either an infinite regress of contingent explanations, or a brute fact.
5. A fourth option is impossible because the PSR demands only two possible kinds of explanations, which will ultimately terminate in 3 logical possibilities.
(Furthermore...)
6. Since brute facts are incompatible with the PSR, and an infinite regress of contingent explanations would require a necessary explanation for the chain's existence, the only real ultimate explanation for the PSR is a necessary one.
7. Since this universe is not logically necessary (necessitarianism is false - per argument below), the last remaining option per the PSR — the necessary option — also fails.
8. Even positing a god who creates/explains the universe doesn't resolve the problem because it is not logically necessary that god create our particular universe.
9. Since the PSR negates all 3 options, the PSR's logic is inherently false.
10. This means one will eventually have to come to the conclusion that brute facts are a necessity. (Even an infinite chain of contingent explanations will itself be a brute fact).
Now some of these steps need further justification.