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, WHICH ARE CORRESPONDENT
TO THEM, AND WHICH THEY EXACTLY REPRESENT.

In seeking for phenomena to prove this proposition, I find only those of
two kinds; but in each kind the phenomena are obvious, numerous, and
conclusive. I first make myself certain, by a new, review, of what I have
already asserted, that every simple impression is attended with a
correspondent idea, and every simple idea with a correspondent