Scientia is knowledge both that and why certain truths are true. It is “knowledge why” based on principles in the light of which what is known could not but be true: the principles “necessitate” the things known. Described like this, scientia is an ideal of both premodern and early modern philosophy. There are rival Scholastic and post-Scholastic interpretations of “knowledge,” “principle,” and “necessitated” that make this way of talking about scientia fit into each tradition.

In Scholastic philosophy, scientia was understood in Aristotle's way as knowledge of the properties of members of natural kinds based on knowledge of the essences of natural kinds. The properties were known by unaided observation. The essences were known by Aristotelian induction. They dawned on one over time with repeated observational exposures to specimens of a kind, and they were expressed by definitions. Scientia located natural kinds in an order of more to less general, which syllogistic explanations of particular explananda recapitulated (cf. Posterior Analytics I.2.71b9). Again, scientia related observed facts to the unfolding of a characteristic natural history of a natural kind. The uncharacteristic or exceptional was not a possible object of scientia. Or, in other words, the causes relevant to scientia were formal and final, not efficient. The ultimate constituents of nature – the elements – were qualitatively defined. Scholastic scientia did not set out to get underneath or above observation, and did not set out to challenge or refine ordinary descriptions of things observed. Instead, it sought to systematize ordinary qualitative observation and description, referring it to definitions per genus et differentia that were no less observational than what they explained.