Since the advent of Hintikka’s Knowledge and Belief [8] in 1962, epistemic logic has become a vibrant and exciting subfield of modal logic. However, like its sister alethic modal logic [18], epistemic logic is not a new invention or dis- covery of the 20th century. In the Middle Ages, philosophers were concerned with many of the same problems in epistemology that exercise us today, and logicians were correspondingly interested in what types of inferences containing epistemic modes or operators are licet