  To operate intelligently in the world, an agent must reason about its
actions. The consequences of an action are a function of both the state of the
world and the action itself. Many aspects of the world are inherently
stochastic, so a representation for reasoning about actions must be able to
express chances of world states as well as indeterminacy in the effects of
actions and other events. This paper presents a propositional temporal
probability logic for representing and reasoning about actions. The logic can
represent the probability that facts hold and events occur at various times. It
can represent the probability that actions and other events affect the future.
It can represent concurrent actions and conditions that hold or change during
execution of an action. The model of probability relates probabilities over
time. The logical language integrates both modal and probabilistic constructs
and can thus represent and distinguish between possibility, probability, and
truth. Several examples illustrating the use of the logic are given.
