It is possible, the skeptic argument declares, for man to be in error;
therefore, it is possible that every individual is in error on every
question. This argument is a non sequitur; it is an equivocation on the term
“possible.”
What is possible to a species under some circumstances, is not necessarily
possible to every individual member of that species under every set of
circumstances. Thus, it is possible for a human being to run the mile in less
than four minutes; and it is possible for a human being to be pregnant. I
cannot, however, go over to a crippled gentleman in his wheelchair and say:
“Perhaps you’ll give birth to a son next week, after you’ve run the mile to the
hospital in 3.9 minutes—after all, you’re human, and it is possible for human
beings to do these things.”
The same principle applies to the possibility of error.