> Your statement is effectively the "Strong PSR"

I would agree with that.

But coming across the Münchhausen trilemma, the idea that all proofs need prior assumptions, or must be one of: (1) a circular argument, (2) an infinite regression, or (3) dogma, I disagree with that.

Some truths are the result of co-constraint. This is where each component of the solution is both an implication of all other components, and an antecedent for all other components. This avoids the trap of being a circular argument, when it can show that any alteration of choices leads to contradiction. Strong proofs of contradiction can be made without infinite regression.

If N co-constrained features can be shown to be consistent, and for N-1 features at least, alternatives to each can be shown to lead to contradiction, then we have a unique solution - it must be the solution. (N-1 comes from the fact, that given co-constraints that lead to one solution, any single feature can be determined by the other N-1.)

That demonstrates that constraint/determination can avoid infinite regression, with recurrent loops of implication, which don't just prove consistency (sufficient), but failure of alternatives (necessity).

Reality must have this form of being. (1) It cannot be determined by any priors or assumptions, because there are no priors. (2) It cannot be determined by infinite regress, because there is no where beyond reality to regress. And obviously, (3) dogma isn't an explanation.

Specific structure must be due to internal consistency (sufficiency), without external or unexplained facts (self-sufficiency), the demonstrated insufficiency or contradiction of any variation or alternative (necessity), and compatibility with our physics (experimental testing that can be made ever more stringent).

> This seems to be framing the speed of light as contingent on other properties of the universe, but that just pushes us back.

I agree. In terms of explaining local physics.

Local properties are most likely to be explainable with the typical regression of explanation, backed up by experimentally verified "axioms", which will then lead to deeper explanations. For local physics, we cannot just prove mathematically that a relationship can work, or even must work, but that the local conditions also require it.

Even a perfect Platonic tautological necessity for a sub-structure of reality, must be experimentally demonstrated to apply locally. We have to establish that we are "there", experimentally.

Even then, in a less pure sense, we may still beneficially use co-constraints, while also regressive knowledge. I.e. explanation = (regressive knowledge) + (co-constraint = circular consistency + inconsistency of alternatives), in order to validate both sufficiency and necessity.

Many proofs of inconsistency can rule out local solutions, without regression. Contradictions are contradictions regardless of priors.

> I could ask what explains the structure of the universe. You can then say that it's logically necessary, which is basically just saying that it's brute but with a heavier burden.

My view is, an explanation of reality will need to demonstrate sufficiency, in terms of being (1) self-consistent, (2) consistent with hosting a region with what we know of our local physics, and (3) to avoid simply being a circular argument, demonstrate that alternatives to the explanation necessarily are contradictory.

Those are three kinds of knowledge to triangulate from.

That would be an approach compatible with strong PSR.

And starting with that, I work from self-containment, self-consistency, and self-determination, as tautological constraints, leveraged as working tautological axioms.

I think it is fair to say, while some may believe a theory of everything with unexplained brut facts can be valid (some things being just what they are), few or none would be unsatisfied with a theory that demonstrated all facts were well determined, was consistent, could be shown to be compatible with our region of reality, and could not be altered without creating a contradiction.

So that is my target.