Bertrand Russell "A History of Western Philosophy - about skepticism -

"Skepticism as a philosophy is not merely doubt, but what may be called dogmatic doubt. The man of science says "I think it is so-and-so, but I am not sure." The man of intellectual curiosity says "I don't know how it is, but I hope to find out." The philosophical Skeptic says "nobody knows and nobody ever can know." It is this element of dogmatism that makes the system vulnerable."

-Bertrand Russell "A History of Western Philosophy" (1945) Book One, Part III, Chapter XXVI, Cynics and Skeptics, p. 234