Why do we call quantum physics an ab initio model?
Because we can use a formal system comprising axiom: Schrodinger equation, derivation rules: integral calculus, statements: assertions on wavefunctions, and symbols: \psi, T, V… to calculate the properties of a given system e.g. a particle in a box. For classical mechanics it is the same: Newton laws are axioms, derivation rules are calculus, statements are the equations of motion and symbols are v, t, m…. The first principles of classical electromagnetism are represented by Maxwell equations.