To understand the term first quantization one must first understand what it means for something to be quantum in the first place. The classical theory of Newton is a second order nonlinear differential equation that gives the deterministic trajectory of a system of mass, m . The acceleration, a , in Newton's second law of motion, F = m a , is the second derivative of the system's position as a function of time. Therefore, it is natural to seek solutions of the Newton equation that are at least second order differentiable.