Philosophy is the study of fundamental questions. Or is it...? Other definitions include "once, everything was philosphical; gradually, things got spun off into their own fields (e.g., math, logic, biology). Philosophy got left behind."; philosophy is thinking; or philosophy is the study of truth. (Other definitions are more easily applied to specific fields - for instance, "ethics is the study of what you should do.") Questions in philosophy tend to be a priori, but what is and isn't a priori changes over time. Many philosophers were also mathematicians, scientists, or other such things; for example, Pythagoras.