We propose that the formal properties of speech, produced under certain circumstances, reflect the underlying mental processes which individuals deploy in problem-solving situations. Our focus is on the ways in which native and non-native speakers of English use tense and aspect when confronting the task of constructing an on-line narrative. When the task becomes difficult speakers attempt to get through it by externalizing their inner order as private speech. It is not only the content of private speech that reveals the speakers' mental activity, however, but the formal properties of this speech also provide insight into the workings of mind. Specifically, we argue that use of the past tense and progressive aspect, under certain circumstances, represents the speakers' attempts to maintain and regain control of their mental activity in the face of a cognitively difficult situation. We will present evidence to show that this is the case for native as well as non-native speakers of a language.