Justification logics are epistemic logics that explicitly include justifications for the agent’s knowledge. The first logic of this kind is the logic of proofs , an explicit counterpart of the modal logic . Indeed, each theorem of ecomes a theorem of if all the terms are replaced with the modality ?; and, vice versa, each theorem of can be transformed into a theorem of if the occurrences of modality are replaced with suitable evidence terms. Instead of statement is known, denoted ? , justification logics reason about justifications for knowledge by using the construct to formalize statements is a justification for , where, dependent on the application, the evidence term can be viewed as an informal justification or a formal mathematical proof.