So that all our complex ideas of substances are imperfect and inadequate. Which would be so also in mathematical figures, if we were to have our complex ideas of them, only by collecting their properties in reference to other figures. How uncertain and imperfect would our ideas be of an ellipsis, if we had no other idea of it, but some few of its properties? Whereas, having in our plain idea the WHOLE essence of that figure, we from thence discover those properties, and demonstratively see how they flow, and are inseparable from it.
- Simple Ideas, [word in Greek], and adequate.
Thus the mind has three sorts of abstract ideas or nominal essences:
First, SIMPLE ideas, which are [word in Greek] or copies; but yet certainly adequate. Because, being intended to express nothing but the power in things to produce in the mind such a sensation, that sensation, when it is produced, cannot but be the effect of that power. So the paper I write on, having the power in the light (I speak according to the common notion of light) to produce in men the sensation which I call white, it cannot but be the effect of such a power in something without the mind; since the mind has not the power to produce any such idea in itself: and being meant for nothing else but the effect of such a power that simple idea is [* words missing] the sensation of white, in my mind, being the effect of that power which is in the paper to produce it, is perfectly adequate to that power; or else that power would produce a different idea.
- Ideas of Substances are Echthypa, and inadequate.
Secondly, the COMPLEX ideas of SUBSTANCES are ectypes, copies too; but not perfect ones, not adequate: which is very evident to the mind, in that it plainly perceives, that whatever collection of simple ideas it makes of any substance that exists, it cannot be sure that it exactly answers all that are in that substance. Since, not having tried all the