The complex ideas that our names of the species of substances properly stand for, are collections of such qualities as have been observed to co exist in an unknown substratum, which we call substance; but what other qualities necessarily co exist with such combinations, we cannot certainly know, unless we can discover their natural dependence; which, in their primary qualities, we can go but a very little way in; and in all their secondary qualities we can discover no connexion at all: for the reasons mentioned, chap.