Newton’s First Law is presented in its traditional form, but strong emphasis is placed on the law as a definition of force. After a short discussion of the history of inertia and the measurement of mass, forces are presented as “a natural constraint or condition that is the cause of alteration of the motion”. The four fundamental forces of nature are described and it is noted that most everyday forces are generalized versions of the electrodynamic force. Physical contact is described as an illusion. A thought experiment is proposed in which the behavior of an object under the influence of multiple forces is debated. Mass is defined as the measurement of inertia and noted to be directly proportional to the weight. Finally, a rough list of forces that one might encounter in physics problems is presented.