This report elucidates the linguistic representation of temporal relations among events. This involves examining sentences that contain two clauses connected by words like once, by the time, when, and before. Specifically, the effect of the tenses of the connected clauses on the acceptability of sentences are examined. For example, Rachel disappeared once Jon had fallen asleep is fine, but *Rachel had disappeared once Jon fell asleep is unacceptable. A theory of acceptability is developed and its implications for interpretation discussed. Factoring of the linguisitic knowledge into a general, syntactic component and a lexical component clarifies the interpretation problem. Finally, a computer model of the theory is demonstrated.