(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., 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.