  The modal approach to the logic of knowledge is, in a sense, built  around the universal quantifier: \(X\) is known in a situation  if \(X\) is true in all situations indistinguishable  from that one. Justifications, on the other hand, bring an  existential quantifier into the picture: \(X\) is known in a  situation if there exists a justification for \(X\) in  that situation. This universal/existential dichotomy is a familiar  one to logicians—in formal logics there exists a proof for a  formula \(X\) if and only if \(X\) is true in all models  for the logic. One thinks of models as inherently non-constructive,  and proofs as constructive things. One will not go far wrong in  thinking of justifications in general as much like mathematical  proofs. Indeed, the first justification logic was explicitly designed to capture mathematical proofs in arithmetic, something which will be discussed further in Section 1.2.