When Bruno was burned at the stake in 1600, philosophers were still inclined to offer natural explanations in Aristotelian terms. Neither the physical proposals of Bruno himself, nor those of other prominent non-Aristotelians like Paracelsus had diminished the power of the explanatory model offered by the scholastics. For those philosophers watching the demise of Bruno in the Campo dei Fiori in Rome, the burning of the wood and its subsequent effects would have been explained adequately in terms of matter and substantial form. For such Aristotelian philosophers, all natural objects are constituted of matter and form, and natural events are explained in terms of the actualization of the potency of these two “principles of nature.” By the time Kenelm Digby composed his Two Treatises of 1644 and Thomas Hobbes his De Corpore in 1655, there was a new explanatory model available to explain such events, one that had greatly diminished the power of the scholastic model. According to the mechanical philosophy, nature is composed of matter—whether the res extensa of Descartes, the atoms of Gassendi, or one of the many less popular accounts of corporeity—whose actions and interactions cause and explain all the phenomena of nature. For the mechanist, therefore, all physical phenomena are to be explained in terms of some kind of matter and motion. Although these thinkers disagreed about how to define the material component in nature, they all took it to be entirely devoid of substantial forms. For our purposes here, it will be helpful to distinguish between first wave and second wave mechanists. A first wave mechanist is someone like Descartes, Galileo, Hobbes, or Gassendi who proposed a version of the mechanical explanatory model before 1650. A second wave mechanist is a philosopher working in the second half of the seventeenth century who accepts the mechanical explanatory model. For our purposes, it is important that many second wave mechanists were prepared to reject the scholastic explanatory model, replace it with the mechanical one, and yet were not content to accept the metaphysical grounding of the mechanical physics offered by the first wave mechanists
