For the ideas that ethics are conversant about, being all real essences, and such as I imagine have a discoverable connexion and agreement one with another; so far as we can find their habitudes and relations, so far we shall be possessed of certain, real, and general truths; and I doubt not but, if a right method were taken, a great part of morality might be made out with that clearness, that could leave, to a considering man, no more reason to doubt, than he could have to doubt of the truth of propositions in mathematics, which have been demonstrated to him.
9.

Our Knowledge of Substances is to be improved, not by contemplation of abstract ideas, but only by Experience.
In our search after the knowledge of SUBSTANCES, our want of ideas that are suitable to such a way of proceeding obliges us to a quite different method.

We advance not here, as in the other, (where our abstract ideas are real as well as nominal essences,) by contemplating our ideas, and considering their relations and correspondences; that helps us very little for the reasons, that in another place we have at large set down.
By which I think it is evident, that substances afford matter 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.