Why is Universal Skepticism a Fallacy?

Skepticism is a practical impossibility.

No sane human being can live without certitude of a practical kind. Even the most confirmed skeptic, no matter how many reasons of a theoretical and speculative nature he may have for doubting the possibility of genuine certitude, cannot lead a human life without denying his skeptical theory all day long in his conduct. 

His life shows that he is certain of so many things: the physical world, with its seasons and changes of weather, with its periods of day and night, with its differences of time and space relations; his own body, in all its concrete reality, in its conditions of health and sickness, in its physical needs of food, drink, and sleep; the existence and knowability of other people and other minds, some of whom agree with him while others disagree, with whom he communicates by means of conversation and writing, and whom he tries to convince of the truth of universal doubt.  

The story is told of Pyrrho the Skeptic that, when chased one day by a rabid dog, he ran for safety without allowing his skepticism to exercise its doubt about the existence and viciousness of the brute. When the bystanders laughed at him and ridiculed him for the inconsistency of his action, he is said to have made the sage remark (completely out of keeping with his theory): "It is difficult to get away entirely from human nature." After all, he could not doubt, in an untheoretical moment, that his body and the dog were real objects. 

This discrepancy between fact and theory, between life and philosophic system, between practical certitude and speculative doubt, is an incontrovertible proof that universal doubt is impossibility except as a mere formulation of the mind. When facts and theories clash and contradict each other in such transparent fashion, the sane man will not deny the facts and cling to his theories, but will realize that something is radically wrong with his views. Facts cannot be denied. To persist in universal skepticism in the face of a million contradicting facts of life bespeaks either insanity or stubbornness of mind. 

When the inconsistency between life and theory cannot be harmonized, it will not do to deny life, because that would be ridiculous; the theory must be abandoned as essentially faulty. Universal skepticism, therefore, must be rejected as a practical impossibility.