Philosophy does not deal in unverified assertions or mere opinions. If it accepts revelations as part of its teaching, it does so only because the revealers have proven themselves to be utterly reliable, only because they have gone through the most strenuous mental emotional and moral discipline. Much of its teaching, however, may be put to the test of evidence and reasoning, and this test is not only welcomed but required.
-- Notebooks Category 20: What Is Philosophy? > Chapter 1: Toward Defining Philosophy > # 80