 Newton was well aware that the Principia’s methodology of discovering the forces present in nature was controversial, and not merely because of questions about action at a distance. So when he revised the text, under the editorship of Roger Cotes, for publication in a second edition in 1713, he added other methodological remarks. These remarks included what Newton called “regulae philosophandi”, or rules of philosophy, which became the focal point of vigorous discussion and debate well into the eighteenth century. The first two rules concern causal reasoning, but it is the third rule that generated the most debate, for it involved both an aspect of Newton’s controversial argument for universal gravity and also a rare public statement by Newton of what he regarded as the “foundation” of natural philosophy. The third rule concerns an induction problem: we have perceptions and experiments that provide us with knowledge of the objects and natural phenomena in our neck of the universe, but on what basis can we reach a conclusion concerning objects and phenomena throughout the rest of the universe? Newton himself reached such a conclusion about gravity in proposition seven of Book III of the Principia. Part of Newton’s answer is presented in rule 3: