From time to time I have awakened from a sort of dream or brain fart in which it seems to me I have acquired a solution to some impossible problem along the lines of the square circle, or in any case come to possess some seemingly significant intention — which unravels into nothing as I awake in the attempt to jot down or otherwise discharge that impulse to an impossible deed.
What if all my understanding — including my grasp of the least dubitable things — is another one of those illusions?
We may call puzzlement of this form the Doubt Of All Doubt.
Doubt of this form directs the skeptic to a limit of coherence, and in this respect promises to cut deeper than more customary arguments from dream and hallucination, which may be said to take for granted the coherence and utility of a language, and a logic, and a worldview.
To press on the borders of coherence in this way is to cast shades of doubt on every judgment.
Sense flickers on the horizon of reason. The right-thinking skeptic merely notes that doubts of this form seem marginally rational to him, and in this respect he can’t entirely rule them out. To the right-thinking skeptic, an attempt to refute, to deny, or to wave off in principle all consideration of such doubts is an arbitrary act of insincerity or confusion inconsistent with the practice of discursive austerity — no less than an attempt to affirm any of the vaguely and marginally conceivable alternatives indicated in these doubts.
As Wittgenstein suggests:
“To be sure there is justification; but justification comes to an end.”
“The difficulty is to realize the groundlessness of our believing.”
“At the foundation of well-founded belief lies belief that is not founded.”
(On Certainty, 192, 166, 253)
Of course the right-thinking skeptic agrees that doubt of this form seems of extremely limited utility. It seems this doubt acquaints us with hard boundaries between the conceivable and the inconceivable, between the coherent and the incoherent, between the demonstrable and the indemonstrable, between genuine certainty and Absolute Certainty. Accordingly it seems to reveal something of the character of the rational imagination, the character of rationality and irrationality, for creatures like us. Perhaps no more than this.
Among dogmatists, the Radical Skeptic jumps to the conclusion that the Doubt Of All Doubt is another support for his absurd denials. The Gothic Philosopher who disfigures his own power of reason with unwarranted faith in Absolute Certainty wages eternal war against the Radical Skeptic, and attempts to refute the Doubt Of All Doubt along with all the arguments of his imaginary nemesis, as if those arguments were not absurd and readily dismissed.
The Cabbage Farm 