To know that something is the case, if closely considered, turns out to be no more than to believe with good evidence that something is the case, and beliefs, however well supported by evidence, do not yield certainty. So the question is, what kind of evidence is sufficient to justify a 'knowledge claim'? And most important of all: What kind of beliefs do qualify as rational? This challenging and refreshingly innovative book addresses certain fundamental questions concerning the rational legitimacy of some widely held beliefs, and provides argument-based answers to such questions, while at the same time encouraging the reader to actively engage with the views put forward and form his/her own judgment. The book is typically discursive rather than merely informative, and introduces philosophy by doing it.