And First as to _ideas_, or _unthinking things_. Our knowledge of these has been very much obscured and confounded, and we have been led into very dangerous errors, by supposing a two-fold existence of sense—the one _intelligible_ or in the mind, the other _real_ and without the mind(665). Whereby unthinking things are thought to have a natural subsistence of their own, distinct from being perceived by spirits. This, which, if I mistake not, hath been shewn to be a most groundless and absurd notion, is the very root of Scepticism; for, so long as men thought that real things subsisted without the mind, and that their knowledge was only so far forth _real_ as it was _conformable to real things_, it follows they could not be certain that they had any real knowledge at all. For how can it be known that the things which are perceived are conformable to those which are not perceived, or exist without the mind(666)? 87. Colour, figure, motion, extension, and the like, considered only as so many _sensations_ in the mind, are perfectly known; there being nothing in them which is not perceived. But, if they are looked on as notes or images, referred to _things_ or _archetypes existing without the mind_, then are we involved all in scepticism. We see only the appearances, and not the real qualities of things. What may be the extension, figure, or motion of anything really and absolutely, or in itself, it is impossible for us to know, but only the proportion or relation they bear to our senses. Things remaining the same, our ideas vary; and which of them, or even whether any of them at all, represent the true quality really existing in the thing, it is out of our reach to determine. So that, for aught we know, all we see, hear, and feel, may be only phantom and vain chimera, and not at all agree with the real things existing in _rerum natura_. All this scepticism(667) follows from our supposing a difference between _things_ and _ideas_, and that the former have a subsistence without the mind, or unperceived. It were easy to dilate on this subject, and shew how the arguments urged by sceptics in all ages depend on the supposition of external objects. [(668)But this is too obvious to need being insisted on.]