Self-Validating Empirical Epistemology?

[Ben Davis]

Technically, it is not an axiom because the counterfactual (not all propositions must be empirically verified) could be true. As an first principle it is self-refuting. It's actually an initial premise. While it serves as a good guide for doing natural science, it is worthless for establishing metaphysical claims such at the nature of being-as-such.

Not quite, Chad. The counterfactual statement would be 'The truthfulness of all propositions must not be empirically validated to count as knowledge'. As a statement, the individual words make sense but as a whole, it sentence has only grammatic veracity
Consequently, the proposition can be held as axiomatic.