The rhetorical function of tense and aspect forms in English-for-Science-and-Technology (EST) texts is not well understood because of the enormous variation in their use. In this paper, a new system of analysis of EST data is proposed. To illustrate this system, some data from previous grammatical-rhetorical interpretations will be re-analyzed in an exemplary fashion. In this analysis it is proposed that each grammatical tense/aspect form in English, including the passive, can be reduced to a unique semantic core that may be combined with one of several event types into which predicate phrases can be classified based on their lexical-aspect properties. In creating texts, events are cognitively assembled into coherent causal networks. One factor determining the degree of coherence between events is the grammatical-aspect form used. Presumably, writers make use of the cognitive potential available through these lexical/grammatical-aspect combinations for different rhetorical purposes. Consequently, previous disparate rhetorical interpretations of predicate phrases used in EST texts will be subsumed and systematized according to their degree of coherence.