acquainted with Colours of all kinds, excepting one particular Shade of Blue, for Instance, which it never has been his fortune to meet with. Let all the different Shades of that Colour, except that single one, be plac'd before him, descending gradually from the deepest to the lightest; 'tis plain, that he will perceive a Blank, where that Shade is wanting, and will be sensible, that there is a greater Distance in that Place betwixt the contiguous Colours than in any other. Now I ask, whether 'tis possible for him, from his own Imagination, to supply this Deficiency, and raise up to himself the Idea of that particular Shade, tho' it had never been convey'd to him by his Senses? I believe there are few but will be of Opinion that he can; and this may serve as a Proof, that the simple Ideas are not always, in every Instance, deriv'd from the correspondent Impressions; tho' this Instance is so particular and singular, that 'tis scarce worth our observing, and does not merit, that for it alone we should alter our general Maxim.
Here, therefore, is a Proposition, which not only seems, in itself, simple and intelligible; but, if properly employ'd, might render every Dispute equally intelligible, and banish all that Jargon, which has so long taken possession of metaphysical Reasonings, and drawn such Disgrace upon them: All Ideas, especially abstract ones, are naturally faint and obscure: The Mind has but a slender Hold of them: They are aptto
