OF THE INFERENCE FROM THE IMPRESSION TO THE IDEA.
'Tis easy to observe, that in tracing this relation, the inference we
draw from cause to effect, is not derived merely from a survey of these
particular objects, and from such a penetration into their essences as
may discover the dependence of the one upon the other. There is no
object which implies the existence of any other, if we consider these
objects in themselves, and never look beyond the ideas which we form
of them. Such an inference would amount to knowledge, and would imply
the absolute contradiction and impossibility of conceiving any thing
different. But as all distinct ideas are separable, 'tis evident there
can be no impossibility of that kind. When we pass from a present
impression to the idea of any object, we might possibly have separated
the idea from the impression, and have substituted any other idea in
its room.
'Tis therefore by _experience_ only that we can infer the existence
of one object from that of another. The nature of experience is this.
We remember to have had frequent instances of the existence of one
species of objects; and also remember, that the individuals of another
species of objects have always attended them, and have existed in a
regular order of contiguity and succession with regard to them. Thus
we remember to have seen that species of object we call _fame_, and to
have felt that species of sensation we call _heat_. We likewise call
to mind their constant conjunction in all past instances. Without any
farther ceremony, we call the one _cause_, and the other _effect_, and
infer the existence of the one from that of the other. In all those
instances from which we learn the conjunction of particular causes and
effects, both the causes and effects have been perceived by the senses,
and are remembered: but in all cases, wherein we reason concerning
them, there is only one perceived or remembered, and the other is
supplied in conformity to our past experience.
Thus, in advancing, we have insensibly discovered a new relation
betwixt cause and effect when we least expected it, and were entirely
employed upon another subject. This relation is their _constant
conjunction_. Contiguity and succession are not sufficient to make us
pronounce any two objects to be cause and effect, unless we perceive
that these two relations are preserved in several instances. We may
now see the advantage of quitting the direct survey of this relation,
in order to discover the nature of that _necessary connexion_ which
makes so essential a part of it. There are hopes, that by this means
we may at last arrive at our proposed end; though, to tell the truth,
this new-discovered relation of a constant conjunction seems to
advance us but very little in our way. For it implies no more than
this, that like objects have always been placed in like relations of
contiguity and succession; and it seems evident, at least at first
sight, that by this means we can never discover any new idea, and can
only multiply, but not enlarge, the objects of our mind. It may be
thought, that what we learn not from one object, we can never learn
from a hundred, which are all of the same kind, and are perfectly
resembling in every circumstance. As our senses show us in one instance
two bodies, or motions, or qualities in certain relations of succession
and contiguity, so our memory presents us only with a multitude of
instances wherein we always find like bodies, motions, or qualities,
in like relations. From the mere repetition of any past impression,
even to infinity, there never will arise any new original idea, such
as that of a necessary connexion; and the number of impressions has in
this case no more effect than if we confined ourselves to one only. But
though this reasoning seems just and obvious, yet, as it would be folly
to despair too soon, we shall continue the thread of our discourse;
and having found, that after the discovery of the constant conjunction
of any objects, we always draw an inference from one object to
another, we shall now examine the nature of that inference, and of the
transition from the impression to the idea. Perhaps 'twill appear in
the end, that the necessary connexion depends on the inference, instead
of the inference's depending on the necessary connexion.
Since it appears, that the transition from an impression present to
the memory or senses to the idea of an object, which we call cause or
effect, is founded on past _experience_, and on our remembrance of
their _constant conjunction_, the next question is, whether experience
produces the idea by means of the understanding or imagination; whether
we are determined by reason to make the transition, or by a certain
association and relation of perceptions. If reason determined us, it
would proceed upon that principle, _that instances, of which we have
had no experience, must resemble those of which we have had experience,
and that the course of nature continues always uniformly the same._
In order, therefore, to clear up this matter, let us consider all the
arguments upon which such a proposition may be supposed to be founded;
and as these must be derived either from _knowledge_ or _probability_,
let us cast our eye on each of these degrees of evidence, and see
whether they afford any just conclusion of this nature.
Our foregoing method of reasoning will easily convince us, that there
can be no _demonstrative_ arguments to prove, _that those instances
of which we have had no experience resemble those of which we have
had experience_. We can at least conceive a change in the course of
nature; which sufficiently proves that such a change is not absolutely
impossible. To form a clear idea of any thing is an undeniable argument
for its possibility, and is alone a refutation of any pretended
demonstration against it.
Probability, as it discovers not the relations of ideas, considered
as such, but only those of objects, must in some respects be founded
on the impressions of our memory and senses, and in some respects on
our ideas. Were there no mixture of any impression in our probable
reasonings, the conclusion would be entirely chimerical: and were there
no mixture of ideas, the action of the mind, in observing the relation,
would, properly speaking, be sensation, not reasoning. 'Tis therefore
necessary, that in all probable reasonings there be something present
to the mind, either seen or remembered; and that from this we infer
something connected with it, which is not seen nor remembered.
The only connexion or relation of objects, which can lead us beyond
the immediate impressions of our memory and senses, is that of cause
and effect; and that because 'tis the only one, on which we can found
a just inference from one object to another. The idea of cause and
effect is derived from _experience_, which informs us, that such
particular objects, in all past instances, have been constantly
conjoined with each other: and as an object similar to one of these
is supposed to be immediately present in its impression, we thence
presume on the existence of one similar to its usual attendant.
According to this account of things, which is, I think, in every
point unquestionable, probability is founded on the presumption of a
resemblance betwixt those objects of which we have had experience, and
those of which we have had none; and therefore 'tis impossible this
presumption can arise from probability. The same principle cannot be
both the cause and effect of another; and this is, perhaps, the only
proposition concerning that relation, which is either intuitively or
demonstratively certain.
Should any one think to elude this argument; and without determining
whether our reasoning on this subject be derived from demonstration or
probability, pretend that all conclusions from causes and effects are
built on solid reasoning: I can only desire that this reasoning may be
produced, in order to be exposed to our examination. It may perhaps
be said, that after experience of the constant conjunction of certain
objects, we reason in the following manner. Such an object is always
found to produce another. 'Tis impossible it could have this effect, if
it was not endowed with a power of production. The power necessarily
implies the effect; and therefore there is a just foundation for
drawing a conclusion from the existence of one object to that of its
usual attendant. The past production implies a power: the power implies
a new production: and the new production is what we infer from the
power and the past production.
'Twere easy for me to show the weakness of this reasoning, were I
willing to make use of those observations I have already made, that
the idea of _production_ is the same with that of _causation_, and
that no existence certainly and demonstratively implies a power in
any other object; or were it proper to anticipate what I shall have
occasion to remark afterwards concerning the idea we form of _power_
and _efficacy_. But as such a method of proceeding may seem either to
weaken my system, by resting one part of it on another, or to breed a
confusion in my reasoning, I shall endeavour to maintain my present
assertion without any such assistance.
It shall therefore be allowed for at moment, that the production of one
object by another in any one instance implies a power; and that this
power is connected with its effect. But it having been already proved,
that the power lies not in the sensible qualities of the cause; and
there being nothing but the sensible qualities present to us; I ask,
why in other instances you presume that the same power still exists,
merely upon the appearance of these qualities? Your appeal to past
experience decides nothing in the present case; and at the utmost
can only prove, that that very object, which produced any other, was
at that very instant endowed with such a power; but can never prove,
that the same power must continue in the same object or collection of
sensible qualities; much less, that a like power is always conjoined
with like sensible qualities. Should it be said, that we have
experience, that the same power continues united with the same object,
and that like objects are endowed with like powers, I would renew my
question, _why from this experience we form any conclusion beyond those
past instances, of which we have had experience_? If you answer this
question in the same manner as the preceding, your answer gives still
occasion to a new question of the same kind, even _in infinitum_; which
clearly proves, that the foregoing reasoning had no just foundation.
Thus, not only our reason fails us in the discovery of the _ultimate
connexion_ of causes and effects, but even after experience has
informed us of their _constant conjunction_, 'tis impossible for
us to satisfy ourselves by our reason, why we should extend that
experience beyond those particular instances which have fallen under
our observation. We suppose, but are never able to prove, that there
must be a resemblance betwixt those objects, of which we have had
experience, and those which lie beyond the reach of our discovery.
We have already taken notice of certain relations, which make us pass
from one object to another, even though there be no reason to determine
us to that transition; and this we may establish for a general rule,
that wherever the mind constantly and uniformly makes a transition
without any reason, it is influenced by these relations. Now, this is
exactly the present case. Reason can never show us the connexion of one
object with another, though aided by experience, and the observation
of their constant conjunction in all past instances. When the mind
therefore passes from the idea or impression of one object to the idea
or belief of another, it is not determined by reason, but by certain
principles, which associate together the ideas of these objects, and
unite them in the imagination. Had ideas no more union in the fancy,
than objects seem to have to the understanding, we could never draw any
inference from causes to effects, nor repose belief in any matter of
fact. The inference therefore depends solely on the union of ideas.
The principles of union among ideas, I have reduced to three general
ones, and have asserted, that the idea or impression of any object
naturally introduces the idea of any other object, that is resembling,
contiguous to, or connected with it. These principles I allow to be
neither the _infallible_ nor the _sole_ causes of an union among ideas.
They are not the infallible causes. For one may fix his attention
during some time on any one object without looking farther. They are
not the sole causes. For the thought has evidently a very irregular
motion in running along its objects, and may leap from the heavens
to the earth, from one end of the creation to the other, without any
certain method or order. But though I allow this weakness in these
three relations, and this irregularity in the imagination; yet I
assert, that the only _general_ principles which associate ideas, are
resemblance, contiguity, and causation.
There is indeed a principle of union among ideas, which at first sight
may be esteemed different from any of these, but will be found at the
bottom to depend on the same origin. When every individual of any
species of objects is found by experience to be constantly united with
an individual of another species, the appearance of any new individual
of either species naturally conveys the thought to its usual attendant.
Thus, because such a particular idea is commonly annexed to such a
particular word, nothing is required but the hearing of that word to
produce the correspondent idea; and 'twill scarce be possible for the
mind, by its utmost efforts, to prevent that transition. In this case
it is not absolutely necessary, that upon hearing such a particular
sound, we should reflect on any past experience, and consider what idea
has been usually connected with the sound. The imagination of itself
supplies the place of this reflection, and is so accustomed to pass
from the word to the idea, that it interposes not a moment's delay
betwixt the hearing of the one, and the conception of the other.
But though I acknowledge this to be a true principle of association
among ideas, I assert it to be the very same with that betwixt the
ideas of cause and effect, and to be an essential part in all our
reasonings from that relation. We have no other notion of cause and
effect, but that of certain objects, which have been _always conjoined_
together, and which in all past instances have been found inseparable.
We cannot penetrate into the reason of the conjunction. We only observe
the thing itself, and always find that, from the constant conjunction,
the objects acquire an union in the imagination. When the impression
of one becomes present to us, we immediately form an idea of its usual
attendant; and consequently we may establish this as one part of the
definition of an opinion or belief, that 'tis _an idea related to or
associated with a present impression_.
Thus, though causation be a _philosophical_ relation, as implying
contiguity, succession, and constant conjunction, yet 'tis only so far
as it is a _natural_ relation, and produces an union among our ideas,
that we are able to reason upon it, or draw any inference from it.