Feser said in his publication, "Scholastic Metaphysics - A Contemporary Introduction" that if we reject the PSR, we're undermining any possibility of rational inquiry. Also in Pruss' paper, "PSR and Probability", he says that a localized version of the PSR or rejection of the PSR entails that we can't rationally estimate the probability of any event.

I'll concede that at best it rejects knowledge of cause and effect, which is the basis for scientific reasoning. However I don't see how just because the PSR is false, our thoughts are true or false.

One could also invoke Schopenhauer's fourfold roots of the PSR, without it entailing theism at all.

  • Seeing how the standard interpretation of quantum mechanics rejects PSR, the grim predictions for rational inquiry and probability seem to be greatly exaggerated. Of course, letting go of PSR should not excuse giving up search for causes too soon, but that makes it a useful psychological and methodological heuristic, not a metaphysical principle. For history and modern perspectives on PSR see SEP.
    – Conifold
    Oct 27, 2019 at 9:32
  • It's more that the PSR doesn't hold at a quantum level. If you check out Pruss' paper, he uses Bayes Theorem to conclude why it would be impossible for us to calculate the probability of any event (which is the case at quantum level). So I don't reckon this critique functions.
    – Metanore
    Oct 27, 2019 at 11:04
  • This is not a critique, more of a suggestion: you should take grandiose claims by authors with an agenda (theistic, in the case of Feser and Pruss) with a grain of salt. If you want a critique of Pruss's arguments specifically it is not hard to find, see e.g. Kleinschmidt (she is a theist, btw), or you can ask a separate question about them. But people were doing probability without PSR, or even metaphysics, before and after QM, whether it was "rational" by Pruss's standards or not. Just a thought.
    – Conifold
    Oct 27, 2019 at 11:23
  • Thank you for the correction. While I do agree that they have a theistic bias, they are philosophers of religion and using the PSR as an argument for God. I have also seen Van Inwagen's argument of the PSR, and the creation of the W-PSR which Pruss desperately holds onto. Though I'll check her out thanks, and the PSR does predate quite back, the concept of it anyways. Leibniz was the one who just gave the concept a name. So we've been using the PSR for the basis of scientific reasoning for ages.
    – Metanore
    Oct 27, 2019 at 11:41
  • No, cognitive faculty may give rise to PSR, e.g. our brains are wired to look for reasons...
    – christo183
    Oct 28, 2019 at 13:52


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