some extremely important laws are simply definitions. for example, the central law of mechanics "f" = "dp"/"dt" (newton's second "law" of mechanics) is often treated as a mathematical definition of force just like newton's first law of mechanics (an object that is at rest stays at rest and an object that is in motion stays in motion unless acted by an out side force). although the concept of force predates newton's law, there was no mathematical definition of force before newton. the principle of least action (or principle of stationary action), schroedinger equation, heisenberg's uncertainty principle, causality and a few other laws also fall into this category (of mathematical definitions).