Descartes’ views on explanation are best approached against the background of traditional and contemporary views on the topic. There are no entries on explanatio or explicatio in the philosophical dictionaries of the early modern period. Normally Scholastic writers talked not about explanations of natural phenomena but about their demonstrations, by way of syllogisms yielding apodictic knowledge of causal dependence (Jardine 1976; Dear 1995, 26–30). By contrast, the etymology of explanation and explication (in English, Latin, and French) reveals related senses of clarifying, removing ambiguities, and making intelligible that do not implicate the notion of demonstration. This range of senses is in Cicero, who refers to physics as explicatio naturae, a label borrowed for the same purpose by some writers in the early modern period. Explicationes appear in Scholastic manuals as commentaries or philosophical explications de texte, not typically as causal accounts of natural phenomena. A Scholastic demonstration is an explicatio to the extent that it interprets and clarifies phenomena in a certain way; an explanation in the new physics is a demonstration to the extent that it yields causal knowledge, whether or not it be scientia strictly understood. Yet demonstration and explanation remain different notions, and the differences between them spotlight important contrasts between Peripatetic physics and the new mechanical philosophies. Proponents of these new philosophies sought mechanical explanations of all kinds of properties, including those manifesting the supposed forms and qualities that for the Scholastics were matters of definition and of specification of essences (see form, substantial and quality, real).

Many proponents of the new natural philosophy, including Descartes, retained the ideal of constructing explanations that would count as scientia, especially when the problem could be mathematized and the solution derived from assured principles. But they also appreciated the difficulties in constructing unqualified scientiae of nature, notably of the biological world (Fouke 1989). Claims to apodictic security became less characteristic of the new mechanical philosophies, where the terms explanation and explication multiplied in tandem with increasing concerns about whether causal intelligibility could ever be strictly demonstrative. Explanations became common coin in the sciences, with demonstrations remaining common coin in mathematics, pure and mixed, though in the latter, unqualified demonstrability depended on the likelihood of causal demonstrations within the physical world. In the empirical sciences, other explanatory values began to displace strict demonstrability, such as intelligibility, simplicity and minimalization of theoretical principles, unification of laws, and high informational content.