 Fourth, it remains unclear how proficient Hume became in mathematics. There is manuscript evidence that he attended George Campbell’s extramural lectures on  fluxions.[2]  These notes require careful study, but Barfoot reports that these manuscripts show “little evidence of the application of fluxions to natural philosophy as such” (1990: 190 fn76). Barfoot is correct to suggest that Hume’s treatment of mathematics shows debts to Berkeley’s criticism of Newton. There is less evidence for Barfoot’s claim that Hume would have had working knowledge of the most technical parts of the Principia.