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law； which has hitherto admitted of no exception。 But there
are other causes； which have been found more irregular and
uncertain； nor has rhubarb always proved a purge； or opium a
soporific to every one； who has taken these medicines。 It is
true； when any cause fails of producing its usual effect；
philosophers ascribe not this to any irregularity in nature；
but suppose； that some secret causes； in the particular
structure of parts； have prevented the operation。 Our
reasonings； however； and conclusions concerning the event
are the same as if this principle had no place。 Being
determined by custom to transfer the past to the future； in
all our inferences； where the past has been entirely regular
and uniform； we expect the event with the greatest
assurance； and leave no room for any contrary supposition。
But where different effects have been found to follow from
causes； which are to exactly similar； all these
various effects must occur to the mind in transferring the
past to the future； and enter into our consideration； when
we determine the probability of the event。 Though we give
the preference to that which has been found most usual； and
believe that this effect will exist； we must not overlook
the other effects； but must assign to each of them a
particular weight and authority； in proportion as we have
found it to be more or less frequent。 It is more probable；
in almost every country of E/UROPE； that there will be
frost sometime in J/ANUARY； than that the weather will
continue open through out that whole month； though this
probability varies according to the different climates； and
approaches to a certainty in the more northern kingdoms。
Here then it seems evident； that； when we transfer the past
to the future； in order to determine the effect； which will
result from any cause； we transfer all the different events；
in the same proportion as they have appeared in the past；
and conceive one to have existed a hundred times； for
instance； another ten times； and another once。 As a great
number of views do here concur in one event； they fortify
and confirm it to the imagination； beget that sentiment
which we call ； and give its object the preference
above the contrary event； which is not supported by an equal
number of experiments； and recurs not so frequently to the
thought in transferring the past to the future。 Let any one
try to account for this operation of the mind upon any of
the received systems of philosophy； and he will be sensible
of the difficulty。 For my part； I shall think it sufficient；
if the present hints excite the curiosity of philosophers；
and make them sensible how defective all common theories are
in treating of such curious and such sublime subjects。
* * * *
SECTION VII。
Of the Idea of Necessary Connexion。
PART I。
T/HE great advantage of the mathematical sciences
above the moral consists in this； that the ideas of the
former； being sensible； are always clear and determinate；
the smallest distinction between them is immediately
perceptible； and the same terms are still expressive of the
same ideas； without ambiguity or variation。 An oval is never
mistaken for a circle； nor an hyperbola for an ellipsis。 The
isosceles and scalenum are distinguished by boundaries more
exact than vice and virtue； right and wrong。 If any term be
defined in geometry； the mind readily； of itself；
substitutes； on all occasions； the definition for the term
defined： Or even when no definition is employed； the object
itself may be presented to the senses； and by that means be
steadily and clearly apprehended。 But the finer sentiments
of the mind； the operations of the understanding； the
various agitations of the passions； though really in
themselves distinct； easily escape us； when surveyed by
reflection； nor is it in our power to recall the original
object； as often as we have occasion to contemplate it。
Ambiguity； by this means； is gradually introduced into our
reasonings： Similar objects are readily taken to be the
same： And the conclusion becomes at last very wide of the
premises。
One may safely； however； affirm； that； if we consider
these sciences in a proper light； their advantages and
disadvantages nearly compensate each other； and reduce both
of them to a state of equality。 If the mind； with greater
facility； retains the ideas of geometry clear and
determinate； it must carry on a much longer and more
intricate chain of reasoning； and compare ideas much wider
of each other； in order to reach the abstruser truths of
that science。 And if moral ideas are apt； without extreme
care； to fall into obscurity and confusion； the inferences
are always much shorter in these disquisitions； and the
intermediate steps； which lead to the conclusion； much fewer
than in the sciences which treat of quantity and number。 In
reality； there is scarcely a proposition in E/UCLID so
simple； as not to consist of more parts； than are to be
found in any moral reasoning which runs not into chimera and
conceit。 Where we trace the principles of the human mind
through a few steps； we may be very well satisfied with our
progress； considering how soon nature throws a bar to all
our enquiries concerning causes； and reduces us to an
acknowledgment of our ignorance。 The chief obstacle；
therefore； to our improvement in the moral or metaphysical
sciences is the obscurity of the ideas； and ambiguity of the
terms。 The principal difficulty in the mathematics is the
length of inferences and compass of thought； requisite to
the forming of any conclusion。 And； perhaps； our progress in
natural philosophy is chiefly retarded by the want of proper
experiments and phaenomena； which are often discovered by
chance； and cannot always be found； when requisite； even by
the most diligent and prudent enquiry。 As moral philosophy
seems hitherto to have received less improvement than either
geometry or physics； we may conclude； that； if there be any
difference in this respect among these sciences； the
difficulties； which obstruct the progress of the former；
require superior care and capacity to be surmounted。
There are no ideas； which occur in metaphysics； more
obscure and uncertain； than those of ； ；
or ； of which it is every
moment necessary for us to treat in all our disquisitions。
We shall； therefore； endeavour； in this section； to fix； if
possible； the precise meaning of these terms； and thereby
remove some part of that obscurity； which is so much
complained of in this species of philosophy。
It seems a proposition； which will not admit of much
dispute； that all our ideas are nothing but copies of our
impressions； or； in other words； that it is impossible for
us to of any thing； which we have not antecedently
； either by our external or internal senses。 I have
endeavoured＇15＇ to explain and prove this proposition； and
have expressed my hopes； that； by a proper application of
i