of very little general knowledge; and the bare contemplation of their abstract ideas will carry us but a very little way in the search of truth and certainty.  What, then, are we to do for the improvement of our knowledge in substantial beings?  Here we are to take a quite contrary course:  the want of ideas of their real essences sends us from our own thoughts to the things themselves as they exist.  Experience here must teach me what reason cannot:  and it is by trying alone, that I can certainly know, what other qualities co-exist with those of my complex idea, v.g. whether that yellow heavy, fusible body I call gold, be malleable, or no; which experience (which way ever it prove in that particular body I examine) makes me not certain, that it is so in all, or any other yellow, heavy, fusible bodies, but that which I have tried.  Because it is no consequence one way or the other from my complex idea:  the necessity or inconsistence of malleability hath no visible connexion with the combination of that colour, weight, and fusibility in any body.  What I have said here of the nominal essence of gold, supposed to consist of a body of such a determinate colour, weight, and fusibility, will hold true, if malleableness, fixedness, and solubility in aqua regia be added to it.  Our reasonings from these ideas will carry us but a little way in the certain discovery of the other properties in those masses of matter wherein all these are to be found.  Because the other properties of such bodies, depending not on these, but on that unknown real essence on which these also depend, we cannot by them discover the rest; we can go no further than the simple ideas of our nominal essence will carry us, which is very little beyond themselves; and so afford us but very sparingly any certain, universal, and useful truths.  For, upon trial, having found that particular piece (and all others of that colour, weight, and fusibility, that I ever tried) malleable, that also makes now, perhaps, a part of my complex idea, part of my nominal essence of gold:  whereby though I make my complex idea to which I affix the name gold, to consist of more simple ideas than before; yet still, it not containing the real essence of any species of bodies, it helps me not certainly to know (I say to know, perhaps it may be to conjecture) the other remaining properties of that body, further than they have a visible connexion with some or all of the simple ideas that make up my nominal essence.  For example, I cannot be certain, from this complex idea, whether gold be fixed or no; because, as before, there is no necessary connexion or inconsistence to be discovered betwixt a complex idea of A body yellow, heavy, fusible, malleable; betwixt these, I say, and fixedness; so that I may certainly know, that in whatsoever body these are found, there fixedness is sure to be.  Here, again, for assurance, I must apply myself to experience; as far as that reaches, I may have certain knowledge, but no further.