Selection from – Ethics – Part IV. Of Human Bondage, or the Strength of the Emotions (Page 25)
Spinoza's Words: (it is a right of nature to advance one's own interests)
VIII. Whatsoever in nature we deem to be evil, or to be capable of injuring our faculty for existing and enjoying the rational life, we may endeavour to remove in whatever way seems safest to us; on the other hand, whatsoever we deem to be good or useful for preserving our being, and enabling us to enjoy the rational life, we may appropriate to our use and employ as we think best. Everyone without exception may, by sovereign right of nature, do whatsoever he thinks will advance his own interest.
Comment:
Spinoza feels safe in declaring that man has a right of nature, do whatsoever he thinks will advance his own interest because he is talking about the rational man who Spinoza knows will not do anything that will harm his fellow man. Indeed the rational man, because he knows he needs his fellow man for his own good, will endeavor to aid him.