Composite and Simple Things

Descartes create a distinction about different things

Composite things - are the things that are complex, always changing, dubious and must be doubt like Physics, Astronomy, and Medicine.

Simple things - are the things that are fixed and unchanging like colors, shapes, quantities, space, time—the kinds of objects studied by Arithmetic and Geometry.

Whenever I'm awake or sleeping 2 plus 3 is always equal to 5. Therefore, Simple things are the things that Rene Descartes can trust.