"By the mere light of reason it seems difficult to prove the immortality of the soul: the arguments for it are commonly derived either from metaphysical topics, or moral, or physical. But in reality it is the gospel, and the gospel alone, that has brought life and immortality to light.[38]
"1. Metaphysical topics suppose that the soul is immaterial, and that 'tis impossible for thought to belong to a material substance.[39] But just metaphysics teach us that the notion of substance is wholly confused and imperfect; and that we have no other idea of any substance, than as an aggregate of particular qualities inhering in an unknown something. Matter, therefore, and spirit, are at bottom equally unknown, and we cannot determine what qualities inhere in the one or in the other.[40] They likewise teach us, that nothing can be decided a priori concerning any cause or effect; and that experience, being the only source of our judgments of this nature, we cannot know from any other principle, whether matter, by its structure or arrangement, may not be the cause of thought. Abstract reasonings cannot decide any question of fact or existence. But admitting a spiritual substance to be dispersed throughout the universe, like the ethereal fire of the Stoics, and to be the only inherent subject of thought, we have reason to conclude from analogy, that nature uses it after the manner she does the other substance, matter. She employs it as a kind of paste or clay; modifies it into a variety of forms or existences; dissolves after a time each modification, and from its substance erects a new form. As the same material substance may successively compose the bodies of all animals, the same spiritual substance may compose their minds: Their consciousness, or that system of thought which they formed during life, may be continually dissolved by death, and nothing interests them in the new modification. The most positive assertors of the mortality of the soul never denied the immortality of its substance; and that an immaterial substance, as well as a material, may lose its memory or consciousness, appears in part from experience, if the soul be immaterial. Seasoning from the common course of nature, and without supposing any new interposition of the Supreme Cause, which ought always to be excluded from philosophy, what is incorruptible must also be ingenerable. The soul, therefore, if immortal, existed before our birth, and if the former existence noways concerned us, neither will the latter. Animals undoubtedly feel, think, love, hate, will, and even reason, though in a more imperfect manner than men: Are their souls also immaterial and immortal?"[41]
Hume next proceeds to consider the moral arguments, and chiefly
" ... those derived from the justice of God, which is supposed to be further interested in the future punishment of the vicious and reward of the virtuous."
But if by the justice of God we moan the same attribute which we call justice in ourselves, then why should either reward or punishment be extended beyond this life?[42] Our sole means of knowing anything is the reasoning faculty which God has given us; and that reasoning faculty not only denies us any conception of a future state, but fails to furnish a single valid argument in favour of the belief that the mind will endure after the dissolution of the body.
" ... If any purpose of nature be clear, we may affirm that the whole scope and intention of man's creation, so far as we can judge by natural reason, is limited to the present life."
To the argument that the powers of man are so much greater than the needs of this life require, that they suggest a future scene in which they can be employed, Hume replies:—
"If the reason of man gives him great superiority above other animals, his necessities are proportionably multiplied upon him; his whole time, his whole capacity, activity, courage, and passion, find sufficient employment in fencing against the miseries of his present condition; and frequently, nay, almost always, are too slender for the business assigned them. A pair of shoes, perhaps, was never yet wrought to the highest degree of perfection that commodity is capable of attaining; yet it is necessary, at least very useful, that there should be some politicians and moralists, even some geometers, poets and philosophers, among mankind. The powers of men are no more superior to their wants, considered merely in this life, than those of foxes and hares are, compared to their wants and to their period of existence. The inference from parity of reason is therefore obvious."
In short, Hume argues that, if the faculties with which we are endowed are unable to discover a future state, and if the most attentive consideration of their nature serves to show that they are adapted to this life and nothing more, it is surely inconsistent with any conception of justice that we should be dealt with, as if we had all along had a clear knowledge of the fact thus carefully concealed from us. What should we think of the justice of a father, who gave his son every reason to suppose that a trivial fault would only be visited by a box on the ear; and then, years afterwards, put him on the rack for a week for the same fault?
Again, the suggestion arises, if God is the cause of all things, he is responsible for evil as well as for good; and it appears utterly irreconcilable with our notions of justice that he should punish another for that which he has, in fact, done himself. Moreover, just punishment bears a proportion to the offence, while suffering which is infinite is ipso facto disproportionate to any finite deed.
"Why then eternal punishment for the temporary offences of so frail a creature as man? Can any one approve of Alexander's rage, who intended to exterminate a whole nation because they had seized his favourite horse Bucephalus?
"Heaven and hell suppose two distinct species of men, the good and the bad; but the greatest part of mankind float betwixt vice and virtue. Were one to go round the world with the intention of giving a good supper to the righteous and a sound drubbing to the wicked, he would frequently be embarrassed in his choice, and would find the merits and demerits of most men and women scarcely amount to the value of either."[43]