So-called ill-formed utterances abound in natural discourse. This paper describes how listeners can understand such utterances in a discourse, including speech hesitations and slips-of-the-tongue. Through analysis of durations of utterances and their succeeding pauses, and of intonation patterns, and also through listener understanding experiments using ill-formed utterances, the following results are obtained. 1) Listeners can understand and memorize speech contents by compensating for the ill-formedness, but pauses are indispensable for the processing. 2) Listeners judge appropriateness of each passage in utterances and pick up significantly important phrases, using intonational peculiarities observed in speech hesitation and truncation.