[jec41]

Deductive reasoning without a fact of reality results in philosophy.

[CarolinaGuitarman]

"Deductive reasoning without a fact of reality results in philosophy."

It can still be useful. I don't agree with you that philosophy is not helpful (unless I am misreading you); epistemology is after all a part of philosophy (metaphysics, to be precise). You are correct though that without a basis in empirical observations, deduction has no way of checking itself against reality.