 
Summary: Epistemic Conditionals, Snakes, and
Stars
Horacio L. Arlo Costa
1 Background
Consider a rational agent X at certain point of time t. X's epistemic state
can be represented in dierent ways. According to the Bayesian tradition, X's
state of belief should be represented by a probability measure dened over some
language L 0 , containing neither modal nor epistemic operators.
A cruder way of modelling X's state of belief can be adopted, namely the
one by which X's epistemic state is represented by a set of sentences of L 0 . 1 The
intended interpretation of such a belief set is that it consists of all the sentences
which X accepts at t.
We will adopt here the simpler model and will suppose also that the ideal of
rationality embodied by X requires the following: (1) X is logically omniscient,
but not necessarily omniscient, (2) X is autoepistemically omniscient, i.e. X
knows what he or she knows and X also knows what he or she does not know,
(3) at any point of time potential epistemic changes of X's view are represented
by epistemic commitments, which are to be understood as functions that express
how the current corpus should change in the presence of suppositional inputs
of certain sort, and (4) X is autoepistemically omniscient with respect to the
