 We have seen that medieval thought included a qualified form of tabula rasa empiricism and a distinctive form of justificatory empiricism, coupled with a broad undersanding of “experience.” There is no need to dwell on explanatory empiricism, for insofar as medieval natural philosophy was influenced by Aristotle it shared his view of scientific explanations. For the most part these did not invoke unobservable entities, such as atoms, but manifest powers of the entities we can perceive  (sect. 3.2).  Medieval thinkers did not deny that we could know about unobservable entities. God, after all, was an unobservable entity, and thinkers such as Aquinas thought that “natural reason” could know something about God, albeit by way of analogy. (William of Ockham [ca. 1285–1347] would later downplay the extent of such knowledge, without dismissing it altogether [Leff 1975: 382–98].) But there were limits to what we could know about the unobservable features of the natural world (Hutchison 1982: 235–36). Aquinas, for instance, appears to endorse Aristotle’s view that when it comes to matters that are “not manifest to the senses” (immanifesta sensui) we should not demand “a certain and necessary demonstration”; a merely possible explanation may be the best we can achieve (Aquinas In Meteor. 1.7 [lect. 11]). One could regard this as a modest kind of explanatory empiricism. But the focus here will be on a different question, namely whether any medievals were cognitive empiricists, denying that we have intellectual powers or capacities giving access to factual knowledge independently of experience. 