Epistemology
The word "epistemology" is derived from the ancient Greek "epistēmē" meaning "knowledge" and the suffix "-logy", meaning "logical discourse" (derived from the Greek word "logos" meaning "discourse"). It is analogue to the German "Wissenschaftslehre" (literally, theory of science) which was introduced by philosophers Johann Fichte and Bernard Bolzano in the late 18th century. The word first appeared in English in 1847 as a translation of the German in New York's "Eclectic Magazine" review of a philosophical novel by German author Jean Paul:
Epistemic modal logic
Epistemic logic also deals with belief, not just knowledge. The basic modal operator is usually written "B" instead of "K". In this case though, the knowledge axiom no longer seems right—agents only sometimes believe the truth—so it is usually replaced with the Consistency Axiom, traditionally called D: