experience are trustworthy and entirely sufficient for practical life, and the aim of the above skeptical deliverances was not to shake belief—­only a fool or a lunatic can doubt in earnest the immutability of nature—­but only to make it clear that it is mere belief, and not, as hitherto held, demonstrative or factual knowledge.  Our doubt is intended to define the boundary between knowledge and belief, and to destroy that absolute confidence which is a hindrance rather than a help to investigation.  We should recognize it as a wise provision of nature that the regulation of our thoughts and the belief in the objective validity of our anticipation of future events have not been confided to the weak, inconstant, inert, and fallacious reason, but to a powerful instinct.  In life and action we are governed by this natural impulse, in spite of all the scruples of the skeptical reason.

[Footnote 1:  Hume distinguishes belief as a form of knowledge from religious faith, both in fact and in name.  In the Treatise—­the passage is wanting in the Enquiry—­our conviction of the external existence of the objects of perception is also ascribed to the former, which later formed Jacobi’s point of departure.  Religious faith is referred to revelation.]

In Hume’s earlier work his destructive critique of the idea of cause is accompanied by a deliverance in a similar strain on the concept of substance, which is not included in the shorter revision.  Substances are not perceived through impressions, but only qualities and powers.  The unknown something which is supposed to have qualities, or in which these are supposed to inhere, is an unnecessary fiction of the imagination.  A permanent similarity of attributes by no means requires a self-identical support for these.  A thing is nothing more than a collection of qualities, to which we give a special name because they are always found together.  The idea of substance, like the idea of cause, is founded in a subjective habit which we erroneously objectify.  The impression from which it has arisen is our inner perception that our thought remains constant in the repeated experience of the same group of qualities (whenever I see sugar, I do the same thing, that is, I combine the qualities white color, sweet taste, hardness, etc., with one another), or the impression of a uniform combination of ideas.  The idea of substance becomes erroneous through the fact that we refer it not to the inner activity of representation, to which it rightly belongs, but to the external group of qualities, and make it a real, permanent substratum for the latter.  Mental substances disappear along with material substances.  The soul or mind is, in reality, nothing more than the sum of our inner states, a collection of ideas which flow on in a continuous and regular stream; it is like a stage, across which feelings, perceptions, thoughts, and volitions are passing while it does not itself come into sight.  A permanent self or