common both to poetry and madness, that the vivacity they bestow on the ideas is not deriv'd from the particular situations or connexions of the objects of these...

But how great soever the pitch may be, to which this vivacity
rises, 'tis evident, that in poetry it never has the same feeling with that
which arises in the mind, when we reason, tho' even upon the lowest
species of probability. The mind can easily distinguish betwixt the one
and the other; and whatever emotion the poetical enthusiasm may give to
the spirits, 'tis still the mere phantom of belief or persuasion. The case is
the same with the idea, as with the passion it occasions. There is no
passion of the human mind but what may arise from poetry; tho' at the
same time the feelings of the passions are very different when excited by
poetical fictions, from what they are when they are from belief and
reality. A passion, which is disagreeable in real life, may afford the
highest entertainment in a tragedy, or epic poem. In the latter case, it lies
not with that weight upon us: It feels less firm and solid: And has no
other than the agreeable effect of exciting the spirits, and rouzing the
attention. The difference in the passions is a clear proof of a like
difference in those ideas, from which the passions are deriv'd. Where the
vivacity arises from a customary conjunction with a present impression;
tho' the imagination may not, in appearance, be so much mov'd; yet
there is always something more forcible and real in its actions, than in
the fervors of poetry and eloquence. The force of our mental actions in
this case, no more than in any other, is not to be measur'd by the
apparent agitation of the mind. A poetical description may have a more
sensible effect on the fancy, than an historical narration. It may collect
more of those circumstances, that form a compleat image or picture. It
may seem to set the object before us in more lively colours. But still the
ideas it presents are different to the feeling from those, which arise from
the memory and the judgment. There is something weak and imperfect
amidst all that seeming vehemence of thought and sentiment, which
attends the fictions of poetry.
We shall afterwards have occasion to remark both the resemblance and
differences betwixt a poetical enthusiasm, and a serious conviction. In
the mean time I cannot forbear observing, that the great difference in
their feeling proceeds in some measure from reflection and general
rules. We observe, that the vigour of conception, which fictions receive
from poetry and eloquence, is a circumstance merely accidental, of which
every idea is equally susceptible; and that such fictions are connected
with nothing that is real. This observation makes us only lend ourselves,
so to speak, to the fiction: But causes the idea to feel very different from
the eternal establish'd persuasions founded on memory and custom.
They are somewhat of the same kind: But the one is much inferior to the
other, both in its causes and effects.
A like reflection on general rules keeps us from augmenting our belief
upon every encrease of the force and vivacity of our ideas. Where an
opinion admits of no doubt, or opposite probability, we attribute to it a
full conviction: tho' the want of resemblance, or contiguity, may render
its force inferior to that of other opinions. 'Tis thus the understanding
corrects the appearances of the senses, and makes us imagine, that an
object at twenty foot distance seems even to the eye as large as one of the
same dimensions at ten.
We may observe the same effect of poetry in a lesser degree; only with
this difference, that the least reflection dissipates the illusions of poetry,
and Places the objects in their proper light. 'Tis however certain, that in
the warmth of a poetical enthusiasm, a poet has a, counterfeit belief, and
even a kind of vision of his objects: And if there be any shadow of
argument to support this belief, nothing contributes more to his full
conviction than a blaze of poetical figures and images, which have their
effect upon the poet himself, as well as upon his readers.


SECT. XI.
Of the Probability of Chances.


But in order to bestow on this system its full force and evidence, we must
carry our eye from it a moment to consider its consequences, and explain
from the same principles some other species of reasoning, which are
deriv'd from the same origin.
Those philosophers, who have divided human reason into knowledge
and probability, and have defin'd the first to be that evidence, which
arises from the comparison of ideas, are oblig'd to comprehend all our
arguments from causes or effects under the general term of probability.
But tho 'every one be free to use his terms in what sense he pleases; and
accordingly in the precedent part of this discourse, I have follow'd this
method of expression; 'tis however certain, that in common discourse we
readily affirm, that many arguments from causation exceed probability,
and may be receiv'd as a superior kind of evidence.' One wou'd appear
ridiculous, who wou'd say, that 'tis only probable the sun will rise to-
morrow, or that all men must dye; tho' 'tis plain we have no further
assurance of these facts, than what experience affords us. For this reason,
'twould perhaps be more convenient, in order at once to preserve the
common signification of words, and mark the several degrees of
evidence, to distinguish human reason into three kinds, viz. that from
knowledge, from proofs, and from probabilities. By knowledge, I mean
the assurance arising from the comparison of ideas. By proofs, those
arguments, which are deriv'd from the relation of cause and effect, and
which are entirely free from doubt and uncertainty. By probability, that
evidence, which is still attended with uncertainty. 'Tis this last species of
reasoning, I proceed to examine.
Probability or reasoning from conjecture may be divided into two kinds,
viz. that which is founded on chance, and that which arises from causes.
We shall consider each of these in order.
The idea of cause and effect is deriv'd from experience, which presenting
us with certain objects constantly conjoin'd with each other, produces
such a habit of surveying them in that relation, that we cannot without a
sensible violence survey them iii any other. On the other hand, as chance
is nothing real in itself, and, properly speaking, is merely the negation of
a cause, its influence on the mind is contrary to that of causation; and 'tis
essential to it, to leave the imagination perfectly indifferent, either to
consider the existence or non-existence of that object, which is regarded
as contingent. A cause traces the way to our thought, and in a manner