Chemistry gradually developed as a separate science in the second half of the eighteenth century thanks to the research conducted by Antoine-Laurent Lavoisier, who gave it new founding methods and principles. Lavoisier accomplished a true revolution that his contemporaries saw as a break with the past. Drawing on the philosophical precepts of the Enlightenment, Lavoisier radically transformed the traditional vision of matter as a compound of a handful of elements: Aristotle's four elements, or, later, the three principles of Paracelsus. According to Lavoisier, the number of elements had to be determined from experimental investigations and the results of chemical analysis. He concluded that at least thirty-three elements or simple substances existed in nature. Modern chemistry is not a direct offshoot of alchemy, although the emerging discipline used the characteristic symbols and instruments of alchemy. In fact, alchemy survived alongside the new chemical science. The roots of modern chemistry lie, instead, in medicine, pharmacy, natural philosophy, mineralogy, and artisanal practices. Modern chemistry was effectively born from the convergence between an entirely new corpus of theoretical knowledge and the empirical knowledge of workmen and craftsmen concerning the characteristics and reactions of substances.