  Epistemic analysis of distributed systems is one of the biggest successes
among applications of logic in computer science. The reason for that is that
agents' actions are necessarily guided by their knowledge. Thus, epistemic
modal logic, with its knowledge and belief modalities (and group versions
thereof), has played a vital role in establishing both impossibility results
and necessary conditions for solvable distributed tasks. In distributed
systems, knowledge is largely attained via communication. It has been standard
in both distributed systems and dynamic epistemic logic to treat incoming
messages as trustworthy, thus, creating difficulties in the epistemic analysis
of byzantine distributed systems where faulty agents may lie. In this paper, we
argue that handling such communication scenarios calls for additional
modalities representing the informational content of messages that should not
be taken at face value. We present two such modalities: hope for the case of
fully byzantine agents and creed for non-uniform communication protocols in
general.
