18. Ideas of substances may be false in reference to existing things.
Thirdly, our complex ideas of substances,
being all referred to patterns in things themselves, may be false. That they are all false, when looked upon as the
representations of the unknown essences of things, is so evident that there needs nothing to be said of it. I shall
therefore pass over that chimerical supposition, and consider them as collections of simple ideas in the mind,
taken from combinations of simple ideas existing together constantly in things, of which patterns they are the
supposed copies; and in this reference of them to the existence of things, they are false ideas:--(1) When they put
together simple ideas, which in the real existence of things have no union; as when to the shape and size that exist
together in a horse, is joined in the same complex idea the power of barking like a dog: which three ideas,
however put together into one in the mind, were never united in nature; and this, therefore, may be called a false
idea of a horse. (2) Ideas of substances are, in this respect, also false, when, from any collection of simple ideas
that do always exist together, there is separated, by a direct negation, any other simple idea which is constantly
joined with them. Thus, if to extension, solidity, fusibility, the peculiar weightiness, and yellow colour of gold,
any one join in his thoughts the negation of a greater degree of fixedness than is in lead or copper, he may be said
to have a false complex idea, as well as when he joins to those other simple ones the idea of perfect absolute
fixedness. For either way, the complex idea of gold being made up of such simple ones as have no union in
nature, may be termed false. But, if he leave out of this his complex idea that of fixedness quite, without either
actually joining to or separating it from the rest in his mind, it is, I think, to be looked on as an inadequate and
imperfect idea, rather than a false one; since, though it contains not all the simple ideas that are united in nature,
yet it puts none together but what do really exist together.
