In this study, the syntactic and semantic features of adverb clauses in English are examined. After having mentioned the difficulties in researching language, it is stated that such difficulties originate from too many uncontrollable and complex variables to be considered in studying language. When writing the grammar of a language, some adequacy criteria should be used. It has been stated that these criteria are observational adequacy, descriptive adequacy and explanatory adequacy. In other words, the explanation of any concept in grammar needs to be backed up by observation, description and logical explanation. It has been observed that neither traditional grammars nor structuralist grammars posses the power to explain grammatical concepts by using these three adequacy criteria. For this reason, in order to examine the issues related to adverbial clauses in English, a generative-transformational approach which considers the three adequacy criteria is adopted in this study.