ab initio method

Q: Why do we call quantum physics an ab initio model? Why do we call classical mechanics an ab initio model? Is classical electromagnetism an an ab initio model (and if it is one, what are its first principles)?
Ans: we call quantum mechanics and classical mechanics an ab initio model because it give basics and formulate from fundamental postulates. classical electromagnetism is also ab initio model because it can dervied from the maxwell equation