The premier reason why people believe the PSR and weaker versions such as the CP is that they take these principles to be self-evident, obvious, intuitively clear, in no need of argumentative support. For instance, when presented with the Parmenidean PSR-based time-shift argument against change, even when the PSR premise is made explicit, most students do not wish to make it be their critical target – sometimes, in fact, it takes quite a while before someone objects to the PSR. The public at large is likely to see the purpose of this book as silly: Why argue for the obvious? Of course once it is shown that the PSR has the implication that there is a necessary being that created the universe, one is more likely to question the PSR. But even then, undergraduate atheists seem to have a certain preference for denying the contingency of the universe rather than questioning the PSR, though of course that might simply depend on the details of presentation to them.

At the same time, the premier reason why the claim that the PSR is self-evident is rejected by philosophers is that to many of them not only does the PSR not seem obvious, but it seems to be actually false, for instance because it is seen as implying the existence of God or the falsity of quantum mechanics. We have seen that the PSR does not imply the falsity of quantum mechanics.