[There is a] dangerous little catch phrase which advises you to keep an “open mind.” This is a very ambiguous term — as demonstrated by a man who once accused a famous politician of having “a wide open mind.” That term is an anti-concept: it is usually taken to mean an objective, unbiased approach to ideas, but it is used as a call for perpetual skepticism, for holding no firm convictions and granting plausibility to anything. A “closed mind” is usually taken to mean the attitude of a man impervious to ideas, arguments, facts and logic, who clings stubbornly to some mixture of unwarranted assumptions, fashionable catch phrases, tribal prejudices — and emotions. But this is not a “closed” mind, it is a passive one. It is a mind that has dispensed with (or never acquired) the practice of thinking or judging, and feels threatened by any request to consider anything.
What objectivity and the study of philosophy require is not an “open mind,” but an active mind — a mind able and eagerly willing to examine ideas, but to examine them critically. An active mind does not grant equal status to truth and falsehood; it does not remain floating forever in a stagnant vacuum of neutrality and uncertainty; by assuming the responsibility of judgment, it reaches firm convictions and holds to them. Since it is able to prove its convictions, an active mind achieves an unassailable certainty in confrontations with assailants — a certainty untainted by spots of blind faith, approximation, evasion and fear.