A Treatise of Human Nature
Having by these divisions given an order and arrangement to our objects, we may now
apply ourselves to consider with the more accuracy their qualities and relations. The first
circumstance, that strikes my eye, is the great resemblance betwixt our impressions and
ideas in every other particular, except their degree of force and vivacity. The one seem to
be in a manner the reflexion of the other; so that all the perceptions of the mind are
double, and appear both as impressions and ideas. When I shut my eyes and think of my
chamber, the ideas I form are exact representations of the impressions I felt; nor is there
any circumstance of the one, which is not to be found in the other. In running over my
other perceptions, I find still the same resemblance and representation. Ideas and
impressions appear always to correspond to each other. This circumstance seems to me
remarkable, and engages my attention for a moment.
Upon a more accurate survey I find I have been carried away too far by the first
appearance, and that I must make use of the distinction of perceptions into simple and
complex, to limit this general decision, that all our ideas and 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.