The incorporation of spin within classical mechanics suggests the following revision: the Euler equations, or the concept of a time-derivative operator relative to different reference frames, should be our new theoretical paradigm.

From here, the existence of formal developments valid both in classical and in quantum mechanics are explored through the analysis of topics such as: the dynamics of a particle with spin acted upon by a torque, the Thomas precession, the equations of evolution for spin, the concept of quantization, the anomalous Zeeman effect and the energy of the spin-orbit interaction.
The obtained results coincide for already-known concepts as well as those found within quantum theories. For example, when considering the evolution of particles with spin within magnetic fields, classical equations of motion present equivalent results as those derived using equations of evolution for expected quantum values.  This means that there are similarities supporting and justifying the point of view adopted in this book. 

The author hopes that the reader may benefit from and enjoy reading this text. For all whom read and enjoy reading this publication, he pass on the words Virgil used when talking about Lucretius, the author of De Rerum Natura, “Fortunate is he who is able to know the causes of things.”