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 ego, as a substratum of ideas, is not perceived; there is no invariable, permanent impression. That which leads to the assumption of personal identity is only the frequent repetition of similar trains of ideas, and the gradual succession of our ideas, which is easily confused with constancy. Thus robbed of its substantiality, the soul has no further claims to immateriality and immortality, and suicide ceases to be a crime.[1] [Footnote 1: Cf. the essays on _Suicide_ and the _Immortality of the Soul_, 1783, whose authorship by Hume, however, is not absolutely established [of. Green and Grose, as above, p. 221, note first.--TR.]]