'Twill here be worth our observation, that the past experience, on which
all our judgments concerning cause and effect depend, may operate on
our mind in such an insensible manner as never to be taken notice of,
and may even in some measure be unknown to us. A person, who stops
short in his journey upon meeting a river in his way, foresees the
consequences of his proceeding forward; and his knowledge of these
consequences is convey'd to him by past experience, which informs him
of such certain conjunctions of causes and effects. But can we think, that
on this occasion he reflects on any past experience, and calls to
remembrance instances, that he has seen or heard of, in order to discover
the effects of water on animal bodies? No surely; this is not the method,
in which he proceeds in his reasoning. The idea of sinking is so closely
connected with that of water, and the idea of suffocating with that of
sinking, that the mind makes the transition without the assistance of the
memory. The custom operates before we have time for reflection. The
objects seem so inseparable, that we interpose not a moment's delay in
passing from the one to the other. But as this transition proceeds from
experience, and not from any primary connexion betwixt the ideas, we
must necessarily acknowledge, that experience may produce a belief and
a judgment of causes and effects by a secret operation, and without being
once thought of. This removes all pretext, if there yet remains any, for
asserting that the mind is convinc'd by reasoning of that principle, that
instances of which we have no experience, must necessarily resemble
those, of which we have. For we here find, that the understanding or
imagination can draw inferences from past experience, without reflecting
on it; much more without forming any principle concerning it, or
reasoning upon that principle.
In general we may observe, that in all the most established and uniform
conjunctions of causes and effects, such as those of gravity, impulse,
solidity, &c. the mind never carries its view expressly to consider any past
experience: Tho' in other associations of objects, which are more rare and
unusual, it may assist the custom and transition of ideas by this
reflection. Nay we find in some cases, that the reflection produces the
belief without the custom; or more properly speaking, that the reflection
produces the custom in an oblique and artificial manner. I explain
myself. 'Tis certain, that not only in philosophy, but even in common
life, we may attain the knowledge of a particular cause merely by one
experiment, provided it be made with judgment, and after a careful
removal of all foreign and superfluous circumstances. Now as after one
experiment of this kind, the mind, upon the appearance either of the
cause or the effect, can draw an inference concerning the existence of its
correlative; and as a habit can never be acquir'd merely by one instance; it
may be thought, that belief cannot in this case be esteem'd the effect of
custom. But this difficulty will vanish, if we consider, that tho' we are
here suppos'd to have had only one experiment of a particular effect, yet
we have many millions to convince us of this principle; that like objects
placed in like circumstances, will always produce like effects; and as this
principle has established itself by a sufficient custom, it bestows an
evidence and firmness on any opinion, to which it can be apply'd. The
connexion of the ideas is not habitual after one experiment: but this
connexion is comprehended under another principle, that is habitual;
which brings us back to our hypothesis. In all cases we transfer our
experience to instances, of which we have no experience, either expressly
or tacitly, either directly or indirectly.
I must not conclude this subject without observing, that 'tis very difficult
to talk of the operations of the mind with perfect propriety and exactness;
because common language has seldom made any very nice distinctions
among them, but has generally call'd by the same term all such as nearly
resemble each other. And as this is a source almost inevitable of
obscurity and confusion in the author; so it may frequently give rise to
doubts and objections in the reader, which otherwise he wou'd never
have dream'd of. Thus my general position, that an opinion or belief is
nothing but a strong and lively idea deriv'd from a present impression
related to it, maybe liable to the following objection, by reason of a little
ambiguity in those words strong and lively. It may be said, that not only
an impression may give rise to reasoning, but that an idea may also have
the same influence; especially upon my principle, that all our ideas are
deriv'd from correspondent impressions. For suppose I form at present
an idea, of which I have forgot the correspondent impression, I am able
to conclude from this idea, that such an impression did once exist; and as
this conclusion is attended with belief, it may be ask'd, from whence are
the qualities of force and vivacity deriv'd, which constitute this belief?
And to this I answer very readily, from the present idea. For as this idea
is not here considered, as the representation of any absent object, but as
a real perception in the mind, of which we are intimately conscious, it
must be able to bestow on whatever is related to it the same quality, call it
firmness, or solidity, or force, or vivacity, with which the mind reflects
upon it, and is assur'd of its present existence. The idea here supplies the
place of an impression, and is entirely the same, so far as regards our
present purpose.
Upon the same principles we need not be surpriz'd to hear of the
remembrance of an idea: that is, of the idea of an idea, and of its force
and vivacity superior to the loose conceptions of the imagination. In
thinking of our past thoughts we not only delineate out the objects, of
which we were thinking, but also conceive the action of the mind in the
meditation, that certain <je-ne-scai-quoi>, of which 'tis impossible to give
any definition or description, but which every one sufficiently
understands. When the memory offers an idea of this, and represents it
as past, 'tis easily conceiv'd how that idea may have more vigour and
firmness, than when we think of a past thought, of which we have no
remembrance.
After this any one will understand how we may form the idea of an
impression and of an idea, and how we way believe the existence of an
impression and of an idea.


SECT. IX.
Of the effects of other relations and other Habits.
However convincing the foregoing arguments may appear, we must not
rest contented with them, but must turn the subject on every side, in