Maintaining that two kinds of ambiguity--ambiguous prepositional phrases and ambiguous modification of conjoined elements--account for a large number of ambiguous sentences in technical writing, this paper presents an algebraic analysis of each kind of ambiguity. It then suggests a number of ways in which each ambiguity may be unclear. By using this kind of analysis, the paper offers ways for a writer to clarify ambiguities and offers rules for the use of the technical writer who discovers such ambiguities while proofreading. (TJ)