 Second, Hume lacks an equivalent to Newton’s Rule 4. Hume is not alone in ignoring rule 4. Even Reid and Priestley, who have much to say about the authority of Newton’s Rules of Reasoning, tend to ignore the fourth rule (Tapper 2002). Adam Smith seems to have been one of few eighteenth century figures to have taken it seriously (Schliesser 2005a and 2005b). Recall (from  section 4.2)  that Newton’s Rule IV can be viewed as (1) an encouragement to find and exploit known deviations from the regularities one has established in order to make them “more exact”. (2) A proposal about how to treat a theory, that is, as true until proven otherwise. Hume seems to have not appreciated the first point at all (Schliesser 2004). On the second point, we have seen that Hume shares Newton’s commitment to fallibilism. But this common commitment also hides an important difference between Hume and Newton which is connected to the observation just made about the contrast between Newton’s third rule and the maxim in the footnote to section XI of EHU. Newton’s fallibilism includes commitment to the truth of the propositions within one’s scientific theory until it is proven to be false. Newton realizes that induction can never be certain for all time; he does anticipate Hume in this respect. But it is also an expression of Newton’s “scientific naturalism”. Empirical science is authoritative until one has empirical reason to refine theory. This means that at any time one risks the danger of going beyond one’s evidence, but this is the methodological price one must pay to make further progress. In his eagerness to combat Newtonian superstition, Hume is willing to be more cautious.