The transcendent is that which we cannot otherwise but believe, yet cannot prove; the a priori principles which, so fundamental, we may not prove, yet we must presuppose to legitimate all else of reality.
What makes something transcendental, if there is anything to be transcendental at all?
A Transcendental Deduction must be found; whereby we prove that an enthymeme is in place in our everyday epistemic practices and metaphysical construals, however; we must not, as a contingent matter, not have proved this relata in any other way.
What kind of things are transcendent? Belief in the external world, possibly induction and the place of other epistemic norms, or other metaphysical beliefs like the endurance of particulars, which, even in the face of rational doubt, we must otherwise assume.