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 regula