appearance similar; this is the main question on which I would insist.
The bread, which I formerly eat, nourished me; that is, a body of such
sensible qualities was, at that time, endued with such secret
powers: but does it follow, that other bread must also nourish me at
another time, and that like sensible qualities must always be attended
with like secret powers? The consequence seems nowise necessary. At
least, it must be acknowledged that there is here a consequence
drawn by the mind; that there is a certain step taken; a process of
thought, and an inference, which wants to be explained. These two
propositions are far from being the same, I have found that such an
object has always been attended with such an effect, and I foresee,
that other objects, which are, in appearance, similar, will be
attended with similar effects. I shall allow, if you please, that
the one proposition may justly be inferred from the other: I know,
in fact, that it always is inferred. But if you insist that the
inference is made by a chain of reasoning, I desire you to produce
that reasoning. The connexion between these propositions is not
intuitive. There is required a medium, which may enable the mind to
draw such an inference, if indeed it be drawn by reasoning and
argument. What that medium is, I must confess, passes my
comprehension; and it is incumbent on those to produce it, who
assert that it really exists, and is the origin of all our conclusions
concerning matter of fact.

  * The word, Power, is here used in a loose and popular sense. The
more accurate explication of it would give additional evidence to this
argument. See Sect. 7.

  30. This negative argument must certainly, in process of time,
become altogether convincing, if many penetrating and able
philosophers shall turn their enquiries this way and no one be ever
able to discover any connecting proposition or intermediate step,
which supports the understanding in this conclusion. But as the
question is yet new, every reader may not trust so far to his own
penetration, as to conclude, because an argument escapes his
enquiry, that therefore it does not really exist. For this reason it
may be requisite to venture upon a more difficult task; and
enumerating all the branches of human knowledge, endeavour to show
that none of them can afford such an argument.

  All reasonings may be divided into two kinds, namely,
demonstrative reasoning, or that concerning relations of ideas, and
moral reasoning, or that concerning matter of fact and existence. That
there are no demonstrative arguments in the case seems evident;
since it implies no contradiction that the course of nature may
change, and that an object, seemingly like those which we have
experienced, may be attended with different or contrary effects. May I
not clearly and distinctly conceive that a body, falling from the
clouds, and which, in all other respects, resembles snow, has yet
the taste of salt or feeling of fire? Is there any more intelligible
proposition than to affirm, that all the trees will flourish in
December and January, and decay in May and June? Now whatever is
intelligible, and can be distinctly conceived, implies no
contradiction, and can never be proved false by any demonstrative
argument or abstract reasoning a priori.

  If we be, therefore, engaged by arguments to put trust in past
experience, and make it the standard of our future judgement, these
arguments must be probable only, or such as regard matter of fact
and real existence, according to the division above mentioned. But
that there is no argument of this kind, must appear, if our
explication of that species of reasoning be admitted as solid and
satisfactory. We have said that all arguments concerning existence are
founded on the relation of cause and effect; that our knowledge of
that relation is derived entirely from experience; and that all our
experimental conclusions proceed upon the supposition that the
future will be conformable to the past. To endeavour, therefore, the
proof of this last supposition by probable arguments, or arguments
regarding existence, must be evidently going in a circle, and taking
that for granted, which is the very point in question.

  31. In reality, all arguments from experience are founded on the
similarity which we discover among natural objects, and by which we
are induced to expect effects similar to those which we have found
to follow from such objects. And though none but a fool or madman will
ever pretend to dispute the authority of experience, or to reject that
great guide of human life, it may surely be allowed a philosopher to
have so much curiosity at least as to examine the principle of human
nature, which gives this mighty authority to experience, and makes
us draw advantage from that similarity which nature has placed among
different objects. From causes which appear similar we expect
similar effects. This is the sum of all our experimental
conclusions. Now it seems evident that, if this conclusion were formed
by reason, it would be as perfect at first, and upon one instance,
as after ever so long a course of experience. But the case is far
otherwise. Nothing so like as eggs; yet no one, on account of this
appearing similarity, expects the same taste and relish in all of
them. It is only after a long course of uniform experiments in any
kind, that we attain a firm reliance and security with regard to a
particular event. Now where is that process of reasoning which, from
one instance, draws a conclusion, so different from that which it
infers from a hundred instances that are nowise different from that
single one? This question I propose as much for the sake of
information, as with an intention of raising difficulties. I cannot
find, I cannot imagine any such reasoning. But I keep my mind still
open to instruction, if any one will vouchsafe to bestow it on me.

  32. Should it be said that, from a number of uniform experiments, we
infer a connexion between the sensible qualities and the secret
powers; this, I must confess, seems the same difficulty, couched in