This article attempts to explain Descartes’ understanding of the possibilities, objectives, and functions of scientific knowledge in the Principia philosophiae. In the standard interpretation the scientific system in the Principia is constructed deductively, but a deeper examination shows that Descartes’ understanding very much resembles the voluntarism of late medieval nominalist theology. He emphasises the contingency of the created world, which at every moment is dependent on the power of God’s that sustains it. Descartes further believes that the infinite God is inaccessible to finite beings, and therefore it is not possible to substantiate scientific knowledge by injecting human reason into the ideas of God, as is the case with Kepler and Galileo. The randomness of the world and the unknowable God significantly contribute to the construction of the system of natural philosophy in the Principia: If the intelligence of the creator and human reason are not in harmony, then experience must enter into the process of knowledge, as only empirically is it possible to discover which of an infinite number of possibilities is manifested. Therefore in Descartes the process of understanding specific natural phenomena resembles a hypothesis that explains perceptible phenomena through the interactions of imperceptible corpuscles. While hypotheses cannot provide true and indisputable knowledge of nature, they can compensate for this inadequacy in a manner that modern philosophy regards as adequate they ensure the maintenance of power over nature.