Three areas of the classical rhetoric of Aristotle, adapted for the modern discourse of inquiry and demonstration, provide a systematic framework for students to understand thought, investigation, and writing in other disciplines: aitia, kairos, and the enthymeme and the example. Aitia, or cause, has four aspects--the material cause, the formal cause, the efficient cause, and the final cause--all of which are components of the thought processes involved in composing. The enthymeme, the substance and body of reasoning, has an underlying causal relationship whereby the theory explains method and fact selection, which together explain the conclusion. Causal reasoning, whether inductive or deductive, is a basic thinking process used in or with other mental operations in what is being called critical thinking. Kairos, the "right time" or "appropriateness," involves grasping the pivotal issue on which a problem or case depends and knowing which techniques or thinking processes to apply to its solution. Since freedom of thought must have a structure within which to operate, students' knowledge of these canons of thought processes will enable them to understand thought, investigation, and writing in other disciplines. (JK)