“The whole modern world is at war with reason; and the tower already reels.”

That peril is that the human intellect is free to destroy itself. Just as one generation could prevent the very existence of the next generation, by all entering a monastery or jumping into the sea, so one set of thinkers can in some degree prevent further thinking by teaching the next generation that there is no validity in any human thought. It is idle to talk always of the alternative of reason and faith. Reason is itself a matter of faith. It is an act of faith to assert that our thoughts have any relation to reality at all. If you are merely a skeptic, you must sooner or later ask yourself the question, “Why should anything go right; even observation and deduction? Why should not good logic be as misleading as bad logic? They are both movements in the brain of a bewildered ape?” The young skeptic says, “I have a right to think for myself.” But the old skeptic, the complete skeptic, says, “I have no right to think for myself. I have no right to think at all.”

There is a thought which stops thought. That is the only thought that ought to be stopped. That is the ultimate evil against which all religious authority was aimed. It only appears at the end of decadent ages like our own: and already Mr. H.G. Wells has raised its ruinous banner; he has written a delicate piece of skepticism called “Doubts of the Instrument.” In this he questions the brain itself, and endeavors to remove all reality from all his won assertions, past, present, and to come. But it was against this remote ruin that all the military systems in religion were originally ranked and rule. The creeds and the crusades, the hierarchies and the horrible persecutions were not organized, as is ignorantly said, for the suppression of reason. They were organized for the difficult defense of reason. Man, by a blind instinct, knew that if once things were wildly questioned, reason could be questioned first. The authority of priests to absolve, the authority of popes to define the authority, even of inquisitors to terrify: these were all only dark defenses erected round one central authority, more undemonstrable, more supernatural than all—the authority of man to think. We know now that this is so; we have no excuse for not knowing it. For we can hear skepticism crashing through the old ring of authorities and at the same moment we can see reason swaying upon her throne. In so far as religion is gone, reason is going. For they are both of the same primary and authoritative kind. They are both methods of proof which cannot themselves be proved. And in the act of destroying the idea of Divine authority we have largely destroyed the idea of that human authority by which we do a long-division sum. With a long and sustained tug we have attempted to pull the mitre off pontifical man; and his head has come off with it.

--G.K. Chesterton, "Orthodoxy"

'Twas on the brain, so to speak.