This historical sequence casts light on the evolution of ontologically naturalist doctrines. In the initial seventeenth-century mechanical phase, there was a tension, as Leibniz observed, between the dominant strict mechanism and interactive dualism. However, once mechanism was replaced by a more liberal understanding of forces in the second Newtonian phase, science ceased to raise any objections to dualism and more generally to non-physical causes of physical effects. As a result, the default philosophical view was a non-naturalist interactive pluralism which recognized a wide range of fundamental non-physical influences, including spontaneous mental influences (or “determinations of the soul” as they would then have been called).