Mechanism is an ancient metaphysical doctrine modernized. The main problem it was meant to solve is that of change. This is how Descartes understood and applied it, and this is what made Boyle advocate it. Mechanism comes in diverse versions, and it is not clear whether the systems of Newton and of Leibniz qualify as variants of mechanism or are too remote from the original for that. At times a few theories appear that are fairly similar to each other, yet they belong to different groupings or families of theories and it is not always clear where to draw the line between families of theories: it is often difficult to judge when two similar theories are variants of each other and when they belong to different families of theories. Thus, some consider the theories of Newton and of Leibniz mechanical and others deem them too different from Descartes’ theory to count as mechanical and they call Newton’s and Leibniz’ theories variants of dynamism (Čapek 1961, 96). As long as there is no measure of proximity of ideas, any answer to this question may count as reasonable. Much later, Faraday, Maxwell, and Einstein suggested a new metaphysical system, according to which atoms are not material but characteristics of fields of force. This surely is dynamism proper.