epistemic principle a principle of rationality applicable to such concepts as knowledge, justification, and reasonable belief. Epistemic principles include the principles of epistemic logic and principles that relate different epistemic concepts to one another, or epistemic concepts to nonepistemic ones (e.g., semantic concepts). Epistemic concepts include the concepts of knowledge, reasonable belief, justification, (epistemic) probability, and other concepts that are used for the purpose of assessing the reasonableness of beliefs and knowledge claims. Epistemic principles can be formulated as principles concerning belief systems or information systems, i.e., systems that characterize a person’s possible doxastic state at a given time; a belief system may be construed as a set of (accepted) propositions or as a system of degrees of belief. It is possible to distinguish two kinds of epistemic principles: (a) principles concerning the rationality of a single belief system, and (b) principles concerning the rational changes of belief. The former include the requirements of coherence and consistency for beliefs (and for probabilities); such principles may be said to concern the statics of belief systems. The latter principles include various principles of belief revision and adjustment, i.e., principles concerning the dynamics of belief systems. See also CLOSURE , KK -THESI. R.Hi.