How does one respond to this argument?It's long but an interesting read. Thanks :)

[Neo-Scholastic]

Fruyain, your critic's objection is pretty basic. In the above exchange you repeatedly put forth, in various ways, the proposition that “The truthfulness of all propositions must be empirically validated to count as knowledge.” You did so as if this proposition was a first principle even though the proposition will admit to no first principles. By its own measure it is a proposition whose truthfulness depends on prior evidence. At best, the proposition is self-referencing and at worst self-defeating.