 As Descartes’ examples indicate, both contingent propositions (e.g., that I exist; that I am thinking) and necessary propositions (e.g., that a triangle is bounded by just three lines; that a sphere is bounded by a single surface) can be intuited (cf. Alanen and Yrjönsuuri 1997 and Alanen 1999). Intuition is a type of intellectual seeing or perception in which the things themselves, not definitions, are directly present before the mind. (Descartes chooses the word “intuition” because in Latin intueor means “to look upon, look closely at, gaze at” and also “to regard, observe, consider, give attention to”.) The evidence of intuition is so direct that it cannot be doubted. Thus, intuition paradigmatically satisfies Descartes’ definition of science as “certain and evident cognition”. It is the most important operation of the method.