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ideas is not a whit more comprehensible： So that； upon the
whole； there appears not； throughout all nature； any one
instance of connexion which is conceivable by us。 All events
seem entirely loose and separate。 One event follows another；
but we never can observe any tie between them。 They seem
； but never 。 And as we can have no
idea of any thing which never appeared to our outward sense
or inward sentiment； the necessary conclusion seems to be
that we have no idea of connexion or power at all； and that
these words are absolutely； without any meaning； when
employed either in philosophical reasonings or common life。
But there still remains one method of avoiding this
conclusion； and one source which we have not yet examined。
When any natural object or event is presented； it is
impossible for us； by any sagacity or penetration； to
discover； or even conjecture； without experience； what event
will result from it； or to carry our foresight beyond that
object which is immediately present to the memory and
senses。 Even after one instance or experiment where we have
observed a particular event to follow upon another； we are
not entitled to form a general rule； or foretell what will
happen in like cases； it being justly esteemed an
unpardonable temerity to judge of the whole course of nature
from one single experiment； however accurate or certain。 But
when one particular species of event has always； in all
instances； been conjoined with another； we make no longer
any scruple of foretelling one upon the appearance of the
other； and of employing that reasoning； which can alone
assure us of any matter of fact or existence。 We then call
the one object； ； the other； 。 We suppose
that there is some connexion between them； some power in the
one； by which it infallibly produces the other； and operates
with the greatest certainty and strongest necessity。
It appears； then； that this idea of a necessary
connexion among events arises from a number of similar
instances which occur of the constant conjunction of these
events； nor can that idea ever be suggested by any one of
these instances； surveyed in all possible lights and
positions。 But there is nothing in a number of instances；
different from every single instance； which is supposed to
be exactly similar； except only； that after a repetition of
similar instances； the mind is carried by habit； upon the
appearance of one event； to expect its usual attendant； and
to believe that it will exist。 This connexion； therefore；
which we in the mind； this customary transition of
the imagination from one object to its usual attendant； is
the sentiment or impression from which we form the idea of
power or necessary connexion。 Nothing farther is in the
case。 Contemplate the subject on all sides； you will never
find any other origin of that idea。 This is the sole
difference between one instance； from which we can never
receive the idea of connexion； and a number of similar
instances； by which it is suggested。 The first time a man
saw the communication of motion by impulse； as by the shock
of two billiard…balls； he could not pronounce that the one
event was ： But only that it was with
the other。 After he has observed several instances of this
nature； he then pronounces them to be 。 What
alteration has happened to give rise to this new idea of
？ Nothing but that he now these events to
be in his imagination； and can readily foretell
the existence of one from the appearance of the other。 When
we say； therefore； that one object is connected with
another； we mean only that they have acquired a connexion in
our thought； and give rise to this inference； by which they
become proofs of each other's existence： A conclusion which
is somewhat extraordinary； but which seems founded on
sufficient evidence。 Nor will its evidence be weakened by
any general diffidence of the understanding； or sceptical
suspicion concerning every conclusion which is new and
extraordinary。 No conclusions can be more agreeable to
scepticism than such as make discoveries concerning the
weakness and narrow limits of human reason and capacity。
And what stronger instance can be produced of the
surprising ignorance and weakness of the understanding than
the present。 For surely； if there be any relation among
objects which it imports to us to know perfectly； it is that
of cause and effect。 On this are founded all our reasonings
concerning matter of fact or existence。 By means of it alone
we attain any assurance concerning objects which are removed
from the present testimony of our memory and senses。 The
only immediate utility of all sciences； is to teach us； how
to control and regulate future events by their causes。 Our
thoughts and enquiries are； therefore； every moment；
employed about this relation： Yet so imperfect are the ideas
which we form concerning it； that it is impossible to give
any just definition of cause； except what is drawn from
something extraneous and foreign to it。 Similar objects are
always conjoined with similar。 Of this we have experience。
Suitably to this experience； therefore； we may define a
cause to be 。 Or in other words 。
The appearance of a cause always conveys the mind； by a
customary transition； to the idea of the effect。 Of this
also we have experience。 We may； therefore； suitably to this
experience； form another definition of cause； and call it；
。 But though both these
definitions be drawn from circumstances foreign to the
cause； we cannot remedy this inconvenience； or attain any
more perfect definition； which may point out that
circumstances in the cause； which gives it a connexion with
its effect。 We have no idea of this connexion； nor even any
distant notion what it is we desire to know； when we
endeavour at a conception of it。 We say； for instance； that
the vibration of this string is the cause of this particular
sound。 But what do we mean by that affirmation？ We either
mean 。 We may
consider the relation of cause and effect in either of these
two lights； but beyond these； we have no idea of it。＇21＇
To recapitulate； therefore； the reasonings of this
section： Every idea is copied from some preceding impression
or sentiment； and where we cannot find any impression； we
may be certain that there is no idea。 In all single
instances of the operation of bodies or minds； there is
nothing that produces any impression； nor consequently can
suggest any idea of power or necessary connexion。 But when
many uniform ins