In this chapter of the Science of Education treatise, Caleb Gattegno asserts that since learners of foreign languages are already fluent in at least one language, they hold all the skills necessary to learn another. And while babies do not learn to speak through teachers, classes, and materials, foreign-language teachers can still optimize this artificial environment to trigger the awarenesses and experiences that lead to fluency. By learning our first language, we have all gained great language expertise. This chapter discusses how one can access this expertise and put it to use in the learning and teaching of foreign languages.