You can’t conceive of a philosophy without using reason. Even if you want to undercut reason, you need to philosophize using reason.
F. H. Bradley hit the nail on the head in his 1893 book Appearance and Reality: “The man who is ready to prove that metaphysical knowledge is wholly impossible has no right here to any answer. He must be referred for conviction to the body of this treatise. And he can hardly refuse to go there, since he himself has, perhaps unknowingly, entered the arena. He is a brother metaphysician with a rival theory of first principles… To say the reality is such that our knowledge cannot reach it, is a claim to know reality; to urge that our knowledge is of a kind which must fail to transcend appearance, itself implies that transcendence.”