  The exemplars of scientific knowledge, to be sure, are conceptual disciplines, not only geometry, but also rational theology, the latter being the quintessential science for the  medievals.[7] Yet for the most part, natural philosophy stands side by side with conceptual disciplines, even into the modern period. Bacon, though associated with induction, accepts the demonstrative conception of scientific knowledge, and so does Galileo, who uses experiments to reveal fundamental principles (though also using them in other  ways).[8] As empirical methods are refined and more widely applied, the belief that natural philosophy can stand under the umbrella of scientia comes under increasing  pressure.[9] Some thinkers resist the pressure, most notably Descartes, who derives his laws of nature by an a priori reflection upon God’s nature, and, placing confidence in these rationalist methods, denies that his third law of nature is undermined by conflicting observations of colliding  bodies.[10] Yet for the experimentalists themselves, including Locke’s mentor, Boyle, observations and experiments are the primary vehicle to knowledge.  (It should be noted, however, that most advocates of experimentalism did not consider speculation wholly illegitimate, instead insisting that it be delayed until considerable experimental and observational evidence had been amassed; see Anstey (2011, pp. 4,5).) It is this approach that puts natural philosophy on the path to Hume’s problem of induction, and that most influences Locke.[11]