 For what is sufficient in the inward Contrivance, to make a new Species? There are some Watches, that are made with four Wheels, others with five: Is this a specifick difference to the Workman? Some have Strings and Physies, and others none; some have the Balance loose, and others regulated by a spiral Spring, and others by Hogs Bristles: Are any, or all of these enough to make a specifick difference to the Workman, that knows each of these, and several other different contrivances, in the internal Constitutions of Watches? ‘Tis certain, each of these hath a real difference from the rest: But whether it be an essential, a specifick difference or no, relates only to the complex Idea, to which the name Watch is given: as long as they all agree in the Idea which that name stands for, and that name does not as a generical name comprehend different Species under it, they are not essentially nor specifically different. (III.vi.39; see also III.vi.30)