It is evident the mind knows not things immediately, but only by the intervention of the ideas it has of them.  Our knowledge, therefore, is real only so far as there is a conformity between our ideas and the reality of things.  But what shall be here the criterion?  How shall the mind, when it perceives nothing but its own ideas, know that they agree with things themselves?  This, though it seems not to want difficulty, yet, I think, there be two sorts of ideas that we may be assured agree with things.

4.  As, First All Simple Ideas are really conformed to Things.

First, The first are simple ideas, which since the mind, as has been showed, can by no means make to itself, must necessarily be the product of things operating on the mind, in a natural way, and producing therein those perceptions which by the Wisdom and Will of our Maker they are ordained and adapted to.  From whence it follows, that simple ideas are not fictions of our fancies, but the natural and regular productions of things without us, really operating upon us; and so carry with them all the conformity which is intended; or which our state requires:  for they represent to us things under those appearances which they are fitted to produce in us:  whereby we are enabled to distinguish the sorts of particular substances, to discern the states they are in, and so to take them for our necessities, and apply them to our uses.  Thus the idea of whiteness, or bitterness, as it is in the mind, exactly answering that power which is in any body to produce it there, has all the real conformity it can or ought to have, with things without us.  And this conformity between our simple ideas and the existence of things, is sufficient for real knowledge.

5.  Secondly, All Complex Ideas, except ideas of Substances, are their own archetypes.

Secondly, All our complex ideas, except those of substances, being archetypes of the mind’s own making, not intended to be the copies of anything, nor referred to the existence of anything, as to their originals, cannot want any conformity necessary to real knowledge.  For that which is not designed to represent anything but itself, can never be capable of a wrong representation, nor mislead us from the true apprehension of anything, by its dislikeness to it:  and such, excepting those of substances, are all our complex ideas.  Which, as I have showed in another place, are combinations of ideas, which the mind, by its free choice, puts together, without considering any connexion they have in nature.  And hence it is, that in all these sorts the ideas themselves are considered as the archetypes, and things no otherwise regarded, but as they are conformable to them.  So that we cannot but be infallibly certain, that all the knowledge we attain concerning these ideas is real, and reaches things themselves.  Because in all our thoughts, reasonings, and discourses of this kind, we intend things no further than as they are conformable to our ideas.  So that in these we cannot miss of a certain and undoubted reality.