This article addresses the issue of whether TESOL should clearly articulate a set of pedagogical principles that challenge the assumption that English language teaching (ELT) should be conducted monolingually through English. This "monolingual principle" emphasizes instructional use of the target language (TL) to the exclusion of students' home language (L1), with the goal of enabling learners to think in the TL with minimal interference from the L1. The monolingual principle initially gained widespread acceptance more than 100 years ago in the context of the "direct method" and has continued to exert a strong influence on various language teaching approaches since that time.