we make our complex ones of substances are all of them (bating only the figure and bulk of some sorts) powers; which being relations to other substances, we can never be sure that we know the powers that are in any one body, till we have tried what changes it is fitted to give to or receive from other substances in their several ways of application: which being impossible to be tried upon any one body, much less upon all, it is impossible we should have adequate ideas of any substance made up of a collection of all its properties.