Isaac Newton's main work, Philosophiae Naturalis Principia Mathematica, published in 1686, is (as stated in its first American edition) a revolution from the thick darkness of the Middle Ages man's struggling spirit... to the investigation of physical and moral truth. It opened up to the human intellect the stupendous realities of the material world. It is a monument, which glows with the immortality of the transcendent mind ... a true creation of genius, in time and beyond time, forever. In this famous work, Newton not only laid the basis for mechanics and developed the theory of gravitation but also formulated a set of rules of scientific reasoning listed in the sidebar. Rules had also been formulated earlier (and, in fact, can be traced back to Aristotle's), but Newton's rules are stricter and clearer than all previous ones and aim directly at science (instead of theology). His rules replaced the former way of thinking, which was burdened by antiquated prejudices and theological dogma and which lacked clear principles and strength of consequences. Remarkably, Newton's rules have remained valid over the centuries, and our modern scientific world would be unthinkable without them. Nevertheless, this foundation is not generally taught in schools, and not all scientists and engineers are aware of its outstanding importance. Therefore, Newton's rules are listed in the sidebar on the next page and discussed here in a more modern way with some personal comments and examples. Ethical and moral aspects (such as truthful reporting, fair citing, and avoiding rashly sensational reports) are not discussed here and are taken for granted.