impressions are resembling. I observe, that many
of our complex ideas never had impressions, that corresponded to them,
and that many of our complex impressions never are exactly copied in
ideas. I can imagine to myself such a city as the New Jerusalem, whose
pavement is gold and walls are rubies, though I never saw any such.
I have seen Paris; but shall I affirm I can form such an idea of that
city, as will perfectly represent all its streets and houses in their
real and just proportions?

I perceive, therefore, that though there is in general a great,
resemblance betwixt our complex impressions and ideas, yet the rule is
not universally true, that they are exact copies of each other. We may
next consider how the case stands with our simple, perceptions. After
the most accurate examination, of which I am capable, I venture to
affirm, that the rule here holds without any exception, and that every
simple idea has a simple impression, which resembles it, and every
simple impression a correspondent idea. That idea of red, which we form
in the dark, and that impression which strikes our eyes in sun-shine,
differ only in degree, not in nature. That the case is the same with
all our simple impressions and ideas, it is impossible to prove by a
particular enumeration of them. Every one may satisfy himself in this
point by running over as many as he pleases. But if any one should deny
this universal resemblance, I know no way of convincing him, but by
desiring him to shew a simple impression, that has not a correspondent
idea, or a simple idea, that has not a correspondent impression. If he
does not answer this challenge, as it is certain he cannot, we may from
his silence and our own observation establish our conclusion.

Thus we find, that all simple ideas and impressions resemble each other;
and as the complex are formed from them, we may affirm in general,
that these two species of perception are exactly correspondent. Having
discovered this relation, which requires no farther examination, I am
curious to find some other of their qualities. Let us consider how they
stand with regard to their existence, and which of the impressions and
ideas are causes, and which effects.

The full examination of this question is the subject of the present
treatise; and therefore we shall here content ourselves with
establishing one general proposition, THAT ALL OUR SIMPLE IDEAS IN
THEIR FIRST APPEARANCE ARE DERIVED FROM SIMPLE IMPRESSIONS