Natural language production comprises a variety of processes that may be grouped under two headings. The conceptualization processes select a conceptual theme for expression. They decide which parts of the theme must be actually communicated to the hearer and which can be left unexpressed: the latter are already present in the hearer's memory or can be inferred by him from what the speaker said. And the conceptual content selected for expression must be organized into a linear sequence of messages so that each is expressible as a complete or partial sentence. The psychological mechanism that accomplishes these tasks I will call the conceptualizer. The second main mechanism is the formulator which maps each input conceptual message into a natural language utterance.