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.]]

Is Hume roundly to be called a skeptic? [1] He never impugned the validity of mathematical reasonings, nor experimental truths concerning matters of fact; in regard to the former his thought is rationalistic, in regard to the latter it is empirical or, more accurately, sensationalistic.  His attitude toward the empirical sciences of nature and of mind is that of a semi-skeptic or probabilist, in so far as they go beyond the establishment of facts to the proof of connections under law and to inferences concerning the future.  Habit is for him a safe guide for life, although it does not go beyond probabilities; absolute knowledge is unattainable for us, but not indispensable.  Toward metaphysics, as an alleged science of the suprasensible, he takes up an entirely negative attitude.  If an argument from experience is to be assured of merely that degree of probability which is sufficient for belief, it must not only have a well-established fact (an impression or memory-image) for its starting point, but, together with its conclusion, it must keep within the limits of possible experience.  The limits of possible experience are also the limits of the knowable; inferences to the continued existence of the soul after death and to the being of God are vain sophistry and illusion.  According to the famous conclusion of the Essay, all volumes which contain anything other than “abstract reasonings concerning quantity or number” or “experimental reasonings concerning matter of fact and existence” deserve to be committed to the flames.  In view of this limitation of knowledge to that which is capable of exact measurement and that which is present in experience, as well of the principle that the elements added by thought are to be sharply distinguished from the positively given (the immediate facts of perception), we must agree with those who call Hume the father of modern positivism.[2]

[Footnote 1:  In the Essay, Hume describes his own standpoint as mitigated or academical skepticism in antithesis to the Cartesian, which from doubt and through doubt hopes to reach the indubitable, and to the excessive skepticism of Pyrrhonism, which cripples the impulse to inquiry.  This moderate skepticism asks us only, after resisting the tendency to unreflecting conclusions, to make a duty of deliberation and caution in judging, and to restrain inquiry within those fields which are accessible to our knowledge, i.e., the fields of mathematics and empirical fact.  In the Treatise Hume had favored a sharper skepticism and extended his doubt more widely, e.g., even to the trustworthiness of geometry.  Cf. on this point Ed. Grimm, Zur Geschichte des Erkenntnissproblems, 1890, p, 559 seq.]