9.  Three sorts of Ideas make our complex ones of Corporeal Substances.

The ideas that make our complex ones of corporeal substances, are of these three sorts.  First, the ideas of the primary qualities of things, which are discovered by our senses, and are in them even when we perceive them not; such are the bulk, figure, number, situation, and motion of the parts of bodies; which are really in them, whether we take notice of them or not.  Secondly, the sensible secondary qualities, which, depending on these, are nothing but the powers those substances have to produce several ideas in us by our senses; which ideas are not in the things themselves, otherwise than as anything is in its cause.  Thirdly, the aptness we consider in any substance, to give or receive such alterations of primary qualities, as that the substance so altered should produce in us different ideas from what it did before; these are called active and passive powers:  all which powers, as far as we have any notice or notion of them, terminate only in sensible simple ideas.  For whatever alteration a loadstone has the power to make in the minute particles of iron, we should have no notion of any power it had at all to operate on iron, did not its sensible motion discover it:  and I doubt not, but there are a thousand changes, that bodies we daily handle have a power to cause in one another, which we never suspect, because they never appear in sensible effects.

10.  Powers thus make a great Part of our complex Ideas of particular Substances.

Powers therefore justly make a great part of our complex ideas of substances.  He that will examine his complex idea of gold, will find several of its ideas that make it up to be only powers; as the power of being melted, but of not spending itself in the fire; of being dissolved in aqua regia, are ideas as necessary to make up our complex idea of gold, as its colour and weight:  which, if duly considered, are also nothing but different powers.  For, to speak truly, yellowness is not actually in gold, but is a power in gold to produce that idea in us by our eyes, when placed in a due light:  and the heat, which we cannot leave out of our ideas of the sun, is no more really in the sun, than the white colour it introduces into wax.  These are both equally powers in the sun, operating, by the motion and figure of its sensible parts, so on a man, as to make him have the idea of heat; and so on wax, as to make it capable to produce in a man the idea of white.

11.  The now secondary Qualities of Bodies would disappear, if we could discover the primary ones of their minute Parts.