Abstract: Reveals the beginnings of several important projects during Descartes's time in the army of Maximilian I, stationed at Ulm. These include the composition of the first part of the Regulae ad directionem ingenii, a general theory of method, which provoked a series of dreams, a doctrine of analysis, a work on solid geometry and figurate numbers and, possibly, the discovery of the sine law of refraction. Discusses the relationship between deduction and intuition, Descartes's doctrine of cognition and that of the Stoics, and Descartes's doctrine of clarity and distinctness in comparison with Aristotle's and Quintillian's doctrine of vividness and particularity.

Keywords: clarity and distinctness, cognition, deduction, doctrine of analysis, geometry, intuition, Regulae, sine law of refraction, theory of method,