Which of the following statements is not true about René Descartes? Select all that apply.

A) Descartes is often regarded as the father of modern philosophy due to his emphasis on the application of reason to achieve certain knowledge.
B) Descartes' philosophical journey started with the famous dictum, "Tabula Rasa," which means "blank slate" in Latin.
C) In his work "Meditations on First Philosophy," Descartes proposed the idea of radical doubt and concluded with the famous statement, "Cogito, ergo sum" ("I think, therefore I am").
D) Descartes made significant contributions to mathematics, including the development of the Cartesian coordinate system.