 When we say that in Prime Matter the potentiality (potentia) for being is the same as the potentiality for not being, we mean that two contraries exist in it at the same opposite times, as for example rain can be and not be, but here in the winter, and here in the summer, and that the causes equally producing these two contingent [facts] must be alternating at equal times, [but] the action of those [causes] takes place generally, and [the causes] are the celestial bodies, and consequently they are causes of that which exists just as of that which does not exist. (LC 67BC TC48)