Key Arguments

• Reason makes no demands contrary to nature; it therefore prescribes self-love, seeking true usefulness, and preserving one’s being.
• Virtue is action according to one’s nature; thus the foundation of virtue is the endeavour to preserve one’s being, and happiness is man’s power of preserving his being.
• Virtue is to be desired for its own sake; there is nothing more excellent or useful for which it should be desired.
• Suicides are weak-minded and overcome by external causes repugnant to their nature.
• We cannot dispense with external things; many external things are useful to us, especially those most in agreement with our nature.
• Two individuals of the same nature united are more powerful; nothing is more useful to man than man.
• Rational men desire for themselves nothing they do not also desire for others, hence are just, faithful, and honourable.

Source Quotes

But, before I begin to prove my Propositions in detailed geometrical fashion, it is advisable to sketch them briefly in advance, so that everyone may more readily grasp my meaning. As reason makes no demands contrary to nature, it demands, that every man should love himself, should seek that which is useful to him—I mean, that which is really useful to him, should desire everything which really brings man to greater perfection, and should, each for himself, endeavour as far as he can to preserve his own being. This is as necessarily true, as that a whole is greater than its part.

(Cf. III. iv.) Again, as virtue is nothing else but action in accordance with the laws of one's own nature (IV. Def. viii.), and as no one endeavours to preserve his own being, except in accordance with the laws of his own nature, it follows, first, that the foundation of virtue is the endeavour to preserve one's own being, and that happiness consists in man's power of preserving his own being; secondly, that virtue is to be desired for its own sake, and that there is nothing more excellent or more useful to us, for the sake of which we should desire it; thirdly and lastly, that suicides are weak—minded, and are overcome by external causes repugnant to their nature. Further, it follows from Postulate iv.,

Further, it follows from Postulate iv., Part II., that we can never arrive at doing without all external things for the preservation of our being or living, so as to have no relations with things which are outside ourselves. Again, if we consider our mind, we see that our intellect would be more imperfect, if mind were alone, and could understand nothing besides itself.

For if, for example, two individuals of entirely the same nature are united, they form a combination twice as powerful as either of them singly. Therefore, to man there is nothing more useful than man—nothing, I repeat, more excellent for preserving their being can be wished for by men, than that all should so in all points agree, that the minds and bodies of all should form, as it were, one single mind and one single body, and that all should, with one consent, as far as they are able, endeavour to preserve their being, and all with one consent seek what is useful to them all. Hence, men who are governed by reason—that is, who seek what is useful to them in accordance with reason, desire for themselves nothing, which they do not also desire for the rest of mankind, and, consequently, are just, faithful, and honourable in their conduct.

Therefore, to man there is nothing more useful than man—nothing, I repeat, more excellent for preserving their being can be wished for by men, than that all should so in all points agree, that the minds and bodies of all should form, as it were, one single mind and one single body, and that all should, with one consent, as far as they are able, endeavour to preserve their being, and all with one consent seek what is useful to them all. Hence, men who are governed by reason—that is, who seek what is useful to them in accordance with reason, desire for themselves nothing, which they do not also desire for the rest of mankind, and, consequently, are just, faithful, and honourable in their conduct. Such are the dictates of reason, which I purposed thus briefly to indicate, before beginning to prove them in greater detail.

Key Concepts

• As reason makes no demands contrary to nature, it demands, that every man should love himself, should seek that which is useful to him
• the foundation of virtue is the endeavour to preserve one's own being, and that happiness consists in man's power of preserving his own being
• that virtue is to be desired for its own sake
• thirdly and lastly, that suicides are weak—minded, and are overcome by external causes repugnant to their nature.
• we can never arrive at doing without all external things for the preservation of our being
• to man there is nothing more useful than man
• Hence, men who are governed by reason—that is, who seek what is useful to them in accordance with reason, desire for themselves nothing, which they do not also desire for the rest of mankind, and, consequently, are just, faithful, and honourable in their conduct.

Context

Ethics, Part IV, Propositions, Note after Prop. XVIII (programmatic sketch of Part IV ethics) (lines 3132–3264)