When studying the two concepts of tense and aspect linguists have commonly kept apart their semantic and syntactic properties. The authors bridge the gap between the semantic and syntactic properties of verb tense and aspect, and suggest a unified account of tense and aspect using Chomsky's Principles and Parameters framework. They compare tense and aspect systems in Romance and Germanic languages, allowing them to hypothesize principles of universal grammar related to tense and aspect, as well as explain language-specific phenomena. "They have achieved results in the area of tense and aspect that go well beyond what had been done previously." Richard Kayne, CUNY (series editor)