the ab initio way

Quantum mechanics, classical mechanics, and classical electromagnetism can all be called ab initio models within their own domains, because each starts from a set of irreducible postulates. For QM, the first principles are the postulates of wavefunctions, operators, and the Schrödinger equation; for classical mechanics, Newton’s laws or the principle of least action; and for electromagnetism, Maxwell’s equations with the Lorentz force law. Each framework is “first principles” in the sense that its assumptions cannot be further reduced within that language, though QM today is regarded as the more fundamental of them.