『エチカ』、第V部、定理41

The first and only foundation of virtue, or the rule of right living is (IV. xxii. Coroll. and xxiv.) seeking one's own true interest. Now, while we determined what reason prescribes as useful, we took no account of the mind's eternity, which has only become known to us in this Fifth Part. Although we were ignorant at that time that the mind is eternal, we nevertheless stated that the qualities attributable to courage and high--mindedness are of primary importance. Therefore, even if we were still ignorant of this doctrine, we should yet put the aforesaid precepts of reason in the first place. Q.E.D.

The general belief of the multitude seems to be different. Most people seem to believe that they are free, in so far as they may obey their lusts, and that they cede their rights, in so far as they are bound to live according to the commandments of the divine law. They therefore believe that piety, religion, and, generally, all things attributable to firmness of mind, are burdens, which, after death, they hope to lay aside, and to receive the reward for their bondage, that is, for their piety and religion; it is not only by this hope, but also, and chiefly, by the fear of being horribly punished after death, that they are induced to live according to the divine commandments, so far as their feeble and infirm spirit will carry them. If men had not this hope and this fear, but believed that the mind perishes with the body, and that no hope of prolonged life remains for the wretches who are broken down with the burden of piety, they would return to their own inclinations, controlling everything in accordance with their lusts, and desiring to obey fortune rather than themselves. Such a course appears to me not less absurd than if a man, because he does not believe that he can by wholesome food sustain his body for ever, should wish to cram himself with poisons and deadly fare; or if, because he sees that the mind is not eternal or immortal, he should prefer to be out of his mind altogether, and to live without the use of reason; these ideas are so absurd as to be scarcely worth refuting.