Doubt is the enemy of Knowing. Descartes was not a skeptic in the classical sense, but he used “doubting” in an attempt to find some claim that could not be doubted, and reconstruct human knowledge on the basis of that claim. Unfortunately, that part of Descartes seems to have resulted in a huge “mind/body” problem for any knowledge, Indeed, even his claim that “I think therefore I am” has subsequently come under some challenge. Although it is not generally emphasized in introductory philosophy classes, Descartes is forced to use a “good God” hypothesis to “salvage” knowledge and the material world. One result has been the mathemization of “reality” (i.e., coordinate geometry as descriptive of “realities”). Sometimes “the math” does not exactly match experimental results. Should one chalk that up to “experimental error” or revise the mathematical technique?