In his Discourse on Method, Descartes wrote that once he had "acquired some general notions respecting Physics," he felt he would be "sinning grievously" by not sharing them with mankind. This is because he held that there was a "general law" that required every man to "promote … the general Good of mankind." In short, Descartes believed that understanding the natural laws of the world could make human beings the "lords and possessors of nature." With this knowledge, Descartes saw a means of improving the lives of human beings. The example he gave was the study of medicine, a tangible benefit of studying nature's laws. Descartes did not think that nature could be mastered in his lifetime, but believed that by establishing first principles, he could point the way toward knowledge that would benefit all mankind.

In short, the work of Descartes formed a foundation for scientific inquiry, which he saw as a moral obligation inasmuch as it advanced the general good of mankind. Of course, to a modern reader, the concept of "mastery of nature" raises ethical questions. These questions existed in Descartes's own day, when they could be crudely applied to the "conquest" of "wilderness" in the Americas and elsewhere. But Descartes was essentially arguing that the pursuit of science was to be undertaken for the benefit of all mankind. He believed that an understanding of the general laws by which he thought nature functioned would improve and extend people's lives. In other words, he sought to establish a "practical" philosophy in place of what he saw as a "speculative" one. For him, this pursuit was in fact a moral obligation.