In actual spoken dialogues, ambiguity is a special case of uncertainty. Uncertainty is the overall standard condition of a speech understanding system, not only because of possible deficiencies in the recognition, but also because people may make mistakes. The system has to have ways to deal with this condition. In SUNDIAL, the strategy chosen is to find the optimal interpretation with regard to context and situational setting, and to use the result of this interpretation in the following system utterance, so that mutual assurance of understanding what was meant is constantly given.

Keywords: speech dialogue, ambiguity, uncertainty, dialogue strategy, semantics, SUNDIAL.