Soundness in text planning has only recently become an issue. [Chapman 87] raised the point that many of the planning systems in use at the time were not formally sound. That is, the planner would assume something is true, instantiate a rule on the basis of that assumption, later find the assumption was wrong, but would fail to retract the rule. This system not only corrects this problem, but in doing so, it uses the soundness principle to eliminate many impossible solutions that otherwise would have been tried, resulting either in backtracking or an incorrect answer.