(UK spelling: scepticism; from Greek σκέψις skepsis, "inquiry") a family of philosophical views that question the possibility of knowledge.

Scientific skepticism or rational skepticism (also spelled scepticism), sometimes referred to as skeptical inquiry, is a position in which one questions the veracity of claims lacking scientific evidence.

Academic skepticism refers to the skeptical period of the Academy dating from around 266 BCE, when Arcesilaus became scholarch, until around 90 BCE, when Antiochus of Ascalon rejected skepticism, although individual philosophers, such as Favorinus and his teacher Plutarch, continued to defend skepticism after this date.

the belief that statements by environmentalists, and the environmental scientists who support them, are false or exaggerated.

(or moral scepticism in British English) a class of meta-ethical theories all members of which entail that no one has any moral knowledge.

a type of skepticism relating to religion.