Radical skepticism (or radical scepticism in British English) is the philosophical position that knowledge is impossible. Radical skeptics hold that doubt exists as to the veracity of every belief and that certainty is therefore never justified. To determine the extent to which it is possible to respond to radical skeptical challenges is the task of epistemology and "the theory of knowledge".
See also Pyrrhonism Cratylism Epistemological nihilism Nihilism Skepticism Ajñana
References
Leavitt, Fred (2021) If Ignorance is Bliss We Should All be Ecstatic. Open Books
Notes The Epistemology Page