3Over the past 40 years, Jim Cummins has originated theories including the interdependence hypothesis, the common underlying proficiency and the distinction between conversational and academic language proficiency, which have had a profound and long-lasting effect on the education of multilingual learners across the world. In this book he traces the development and impact of these theories, and addresses the critiques they have received and their subsequent implications on his thinking and the application of his theories in classrooms and in policy. In discussing his own theories, Jim Cummins develops a schema for evaluating theoretical concepts - empirical adequacy, logical coherence, and consequential validity - and applies these to current translanguaging theories, evaluating which theory meets the criteria of theoretical legitimacy more adequately.