For all those powers that we take cognizance of, terminating only in the alteration of some sensible qualities in those subjects on which they operate, and so making them exhibit to us new sensible ideas, therefore it is that I have reckoned these powers amongst the simple ideas which make the complex ones of the sorts of substances; though these powers considered in themselves, are truly complex ideas.

And in this looser sense I crave leave to be understood, when I name any of these POTENTIALITIES among the simple ideas which we recollect in our minds when we think of PARTICULAR SUBSTANCES.

For the powers that are severally in them are necessary to be considered, if we will have true distinct notions of the several sorts of substances.
8.

And why.
Nor are we to wonder that powers make a great part of our complex ideas of substances; since their secondary qualities are those which in most of them serve principally to distinguish substances one from another, and commonly make a considerable part of the complex idea of the several sorts of them.

For, our senses failing us in the discovery of the bulk, texture, and figure of the minute parts of bodies, on which their real constitutions and differences depend, we are fain to make use of their secondary qualities as the characteristical notes and marks whereby to frame ideas of them in our minds, and distinguish them one from another: all which secondary qualities, as has been shown, are nothing but bare powers.