If causality is a category of perception as Kant claims why are so many scientists unfazed intellectually by the claim that the Big Bang theory must be an incomplete theory of the universe because the existence of the big bang must have been caused by something prior to the big bang? Personally I side against the scientists in my firm belief that they are defying commonsense in their rejection of the idea that the existence of the universe at the time of the big bang must have had a prior cause. So scientists seem to be rejecting the idea that all occurrences have a cause.

According to Kant, causality is among the organizing concepts through which our mind unifies its experience. Like space and time, causality as well is then not objective (i.e. wholly independent of our mind), but still "empirically" objective in the sense that we cannot help but structure and anticipate the world of our experience as causally ordered.

This sort of account explains your "firm belief" that an uncaused cause defies commonsense. But it also cautions us against claiming any knowledge of what the world might really be like, apart from how our mental faculties are organizing it for us.

The very strength of our conviction that nothing like an uncaused Big Bang could possibly have happened -- the strong feeling that we know this "a priori" -- would suggest to Kant that this belief discloses something about ourselves (about our way of organizing and unifying experience) rather about the world we inhabit.

And so physicists could actually appeal to Kant in rejecting your belief as a constraint on their theorizing much like they might appeal to Kant when they set aside the constraint that their theorizing must present space as Euklidean.

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