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