Skepticism or scepticism (see spelling differences) has many definitions, but generally refers to any questioning attitude towards knowledge, facts, or opinions/beliefs stated as facts, or doubt regarding claims that are taken for granted elsewhere. The word may characterize a position on a single matter, as in the case of religious skepticism, which is "doubt concerning basic religious principles (such as immortality, providence, and revelation)", but philosophical skepticism is an overall approach that requires all information to be well supported by evidence. Skeptics may even doubt the reliability of their own senses. Classical philosophical skepticism derives from the 'Skeptikoi', a school who "asserted nothing". Adherents of Pyrrhonism, for instance, suspend judgment in investigations.