Formal introductions to language study focus on transcribed speech, initially involving a familiar language where words and sentences seem self-evident. Presented this way, language seems to reflect an "autonomous" mental system separate from speech, which can be studied through writing signs. The arguments used to support this approach were originally formulated by Saussure and relate to nineteenth-century views of a localized language faculty in the brain. These influential arguments bolstered the concept of a speech–language division to the point that, at the turn of the twentieth century, many analysts saw instrumental observations of speech as irrelevant. In reviewing these arguments, evidence is discussed showing that the speech–language division is neither physiologically grounded nor methodologically useful in explaining the nature of features and structures of spoken language. One illustration is a study by Lindblom that shows that properties of the hearing system can shape vowel systems. Another example is given in a chapter bearing on how properties of motor speech can shape symbolic signs.