knocked down

Since at least Thomas Aquinas that Catholic doctrine has held that every man can reach truth through reason and faith. The arbiter of truth is a single man himself, supposed to be the most learned of all men - the Pope.

Kant argued in The Critique of Pure Reason that man cannot individually reach truth. Perception takes place through certain categories of the mind which distort reality. Man can never know things-in-themselves (noumena) but only appearences of them (phenomena). Judgements about reality involve a subjective element which make themselves subjective.

Individual judgements about reality are mere persuasions or illusions. Only if such judgements are shared by a number of people do they become convictions and can be said to be true (see here).

Truth can never lie with a single man. It is an attribute of the crowd. The role of the Pope is thus knocked down. This is Kant at his best - the anti-Catholic ideologue.