Quantum Physics is called an ab initio (“from the beginning”) model because its predictions, like the structure of atoms or molecular bonds, are calculated directly from its first principles (the Schrödinger equation and the postulates of quantum mechanics) without needing input from other theories or experimental data for the fundamental equations.

Classical Mechanics is also an ab initio model. Given a specific force (e.g., gravity: F = -GMm/r²), its predictions for motion are calculated directly from Newton’s Laws of Motion (F=ma, etc.). The laws are the first principles; the specific force law is an initial condition.

Classical Electromagnetism is absolutely an ab initio model. Its predictions for electric circuits, light propagation, and antenna radiation are calculated directly from its first principles, which are Maxwell’s Equations:

Gauss’s Law (electric field)

Gauss’s Law for Magnetism

Faraday’s Law of Induction

Ampère’s Law (with Maxwell’s addition)

These four equations, along with the Lorentz Force Law (F = q(E + v × B)), form the complete and fundamental basis of the entire theory