Fluxions the Point of firſt importance, and which paves the way to the reſt, is to find the Fluxion of a Product of two indeterminate Quantities, ſo in the calculus differentialis (which Method is ſuppoſed to have been borrowed from the former with ſome ſmall Alterations) the main Point is to obtain the difference of ſuch Product. Now the Rule for this is got by rejecting the Product or Rectangle of the Differences. And in general it is ſuppoſed, that no Quantity is bigger or leſſer for the Addition or Subduction of its Infiniteſimal: and that conſequently no error can ariſe from ſuch rejection of Infiniteſimals.
XIX. And yet it ſhould ſeem that, whatever errors are admitted in the Premiſes, proportional errors ought to be apprehended in the Concluſion, be they finite or infiniteſimal: and that therefore the ἀχρίβεια of Geometry requires nothing ſhould be neglected or rejected. In anſwer to this you will perhaps ſay, that the Concluſions are accurately true, and that therefore the Principles and Methods from whence they are derived muſt be ſo too.
