Selection from – Ethics – Part III. On the Nature and Origin of the Emotions (Page 20)
Spinoza's Words: (preservation of individual existence - the basis for morality)
I. Desire is the actual essence of man.
Explanation.—We have said that desire is appetite, with consciousness thereof; further, that appetite is the essence of man, in so far as it is determined to act in a way tending to promote its own persistence.
I have take care to define it in such a manner, as to comprehend, under one head, all those endeavours of human nature, which we distinguish by the terms appetite, will, desire, or impulse.
By the term desire, then, I mean all man's endeavours, impulses, appetites, and volitions, which vary according to each man's disposition, and are, therefore, not seldom opposed one to another, according as a man is drawn in different directions, and knows not where to turn.
Comment:
Appetite, desire, will, impulse, volition, essence – take your pick. Our lives are so compounded that more than one of the above is operating at the same time and driving us in contrary directions. Hence our mental anxiety. An important point Spinoza is making is that the basic endeavor of an individual is to promote his own continued existence. I cannot stress this basic realization enough. It is the rock on which Spinoza's whole ethical philosophy rests.
Further on, in Section IV, he says that Nature demands nothing more of us as individuals but that we should strive to maintain our own existence. But it demands nothing less. Spinoza did not know anything about evolution. He did not know that Nature, through the natural selection process, has eliminated those organisms without that internal demand to live and has left within each of us the strongest of desires - to extend our lives. Yet he intuited that that was the universal driving force of humans. Today we recognize it is true of all living things.
What is crucial to understand is that from this true observation Spinoza builds the most rational ethical system known to philosophy. To preserve one's own being sounds like the most selfish of goals yet in Spinoza's rational extension of it it becomes admirable. We have to move deeper into his thought to see how he does it.