Inspired by the success of the distributed computing community in appl
ying logics of knowledge and time to reasoning about distributed proto
cols,we aim for a similarly powerful and high-level abstraction when r
easoning about control problems involving uncertainty. This paper conc
entrates on robot motion planning with uncertainty in both control and
sensing, a problem that has already been well studied within the robo
tics community. First, a new and natural problem in this domain is def
ined: Does there exists a sound and complete termination condition for
a motion, given initial and goal locations? If yes, how to construct
it? Then we define a high-level language, a logic of time and knowledg
e, which we use to reason about termination conditions and to state ge
neral conditions for the existence of sound and complete termination c
onditions in a broad domain. Finally, we show that sound termination c
onditions that are optimal in a precise sense provide a natural exampl
e of knowledge-based programs with multiple implementations.