Wikipedia is the world's newest, largest, most varied, most participatory, and most controversial encyclopedia. It is composed and edited entirely by volunteer netizens; as of November 2004, there were some 29,000 "Wikipedians" writing for it in 109 different languages. The site's massive archive, including 380,000 articles in English alone, puts even Britannica to shame. If you don't see an article addressing your passion for miniature-teapot collecting, don't fret. Just write one.

Among Wikipedia's many unusual aspects is that its cocreator, Larry Sanger, is a professional epistemologist -- a philosopher who explores the very nature and sources of knowledge and who, like many before him, once questioned the possibility of knowing anything with certainty. Sanger says that as a bookish teenager growing up in Anchorage, AK, he decided to model himself after Descartes and become a devout doubter, believing only the things that he could directly perceive or that could be logically derived from what he perceived. "These were the thoughts of a 17-year-old," smiles Sanger, who's now 36. But eventually, he says, he began to realize that some truths cannot be observed: "If the very project of seeking the truth required that I assumed something, then I would assume that."