Thus the ideas of heat and cold, light and darkness, white and black, motion and rest, are equally clear and positive ideas in the mind; though, perhaps, some of the causes which produce them are barely privations, in those subjects from whence our senses derive those ideas.  These the understanding, in its view of them, considers all as distinct positive ideas, without taking notice of the causes that produce them:  which is an inquiry not belonging to the idea, as it is in the understanding, but to the nature of the things existing without us.  These are two very different things, and carefully to be distinguished; it being one thing to perceive and know the idea of white or black, and quite another to examine what kind of particles they must be, and how ranged in the superficies, to make any object appear white or black.

3.  We may have the ideas when we are ignorant of their physical causes.

A painter or dyer who never inquired into their causes hath the ideas of white and black, and other colours, as clearly, perfectly, and distinctly in his understanding, and perhaps more distinctly, than the philosopher who hath busied himself in considering their natures, and thinks he knows how far either of them is, in its cause, positive or privative; and the idea of black is no less positive in his mind than that of white, however the cause of that colour in the external object may be only a privation.

4.  Why a privative cause in nature may occasion a positive idea.

If it were the design of my present undertaking to inquire into the natural causes and manner of perception, I should offer this as a reason why a privative cause might, in some cases at least, produce a positive idea; viz. that all sensation being produced in us only by different degrees and modes of motion in our animal spirits, variously agitated by external objects, the abatement of any former motion must as necessarily produce a new sensation as the variation or increase of it; and so introduce a new idea, which depends only on a different motion of the animal spirits in that organ.

5.  Negative names need not be meaningless.

But whether this be so or not I will not here determine, but appeal to every one’s own experience, whether the shadow of a man, though it consists of nothing but the absence of light (and the more the absence of light is, the more discernible is the shadow) does not, when a man looks on it, cause as clear and positive idea in his mind, as a man himself, though covered over with clear sunshine?  And the picture of a shadow is a positive thing.  Indeed, we have negative names, to which there be no positive ideas; but they consist wholly in negation of some certain ideas, as silence, invisible; but these signify not any ideas in the mind but their absence.

6.  Whether any ideas are due to causes really private.