Therefore these complex ideas of modes, which they are referred by the mind, and intended to correspond to the ideas in the mind of some other intelligent being, expressed by the names we apply to them, they may be very deficient, wrong, and inadequate; because they agree not to that which the mind designs to be their archetype and pattern:  in which respect only any idea of modes can be wrong, imperfect, or inadequate.  And on this account our ideas of mixed modes are the most liable to be faulty of any other; but this refers more to proper speaking than knowing right.

6.  Ideas of Substances, as referred to real Essences, not adequate.

Thirdly, what ideas we have of substances, I have above shown.  Now, those ideas have in the mind a double reference:  1.  Sometimes they are referred to a supposed real essence of each species of things. 2.  Sometimes they are only designed to be pictures and representations in the mind of things that do exist, by ideas of those qualities that are discoverable in them.  In both which ways these copies of those originals and archetypes are imperfect and inadequate.

First, it is usual for men to make the names of substances stand for things as supposed to have certain real essences, whereby they are of this or that species:  and names standing for nothing but the ideas that are in men’s minds, they must constantly refer their ideas to such real essences, as to their archetypes.  That men (especially such as have been bred up in the learning taught in this part of the world) do suppose certain specific essences of substances, which each individual in its several kinds is made conformable to and partakes of, is so far from needing proof that it will be thought strange if any one should do otherwise.  And thus they ordinarily apply the specific names they rank particular substances under, to things as distinguished by such specific real essences.  Who is there almost, who would not take it amiss if it should be doubted whether he called himself a man, with any other meaning than as having the real essence of a man?  And yet if you demand what those real essences are, it is plain men are ignorant, and know them not.  From whence it follows, that the ideas they have in their minds, being referred to real essences, as to archetypes which are unknown, must be so far from being adequate that they cannot be supposed to be any representation of them at all.  The complex ideas we have of substances are, as it has been shown, certain collections of simple ideas that have been observed or supposed constantly to exist together.  But such a complex idea cannot be the real essence of any substance; for then the properties we discover in that body would depend on that complex idea, and be deducible from it, and their necessary connexion with it be known; as all properties of a triangle depend on, and, as far as they are discoverable, are deducible from the complex idea of three lines including a space.