Selection from – Ethics – Part III. On the Nature and Origin of the Emotions (Page 18)
Spinoza's Words: (to each animal, as to each person, emotions vary according to their natures)
Note.—The emotions of animals are called irrational only differ from man's emotions, to the extent that brute nature differs from human nature. Horse and man are alike carried away by the desire of procreation; but the desire of the former is equine, the desire of the latter is human. So also the lusts and appetites of insects, fishes, and birds must needs vary according to the several natures. Thus, although each individual lives content and rejoices in that nature belonging to him wherein he has his being, yet the [joy of one]...differs in nature from the joy of another, to the extent that the essence of one differs from the essence of another. Lastly, it follows that there is no small difference between the joy which actuates, say, a drunkard, and the joy possessed by a philosopher, as I just mention here by the way. Thus far I have treated of the emotions attributable to man, in so far as he is passive. It remains to add a few words on those attributable to him in so far as he is active.
Comment:
It is interesting to note that Spinoza gives evidence of his advanced ideas in philosophy and biology by ascribing emotions to animals and even to insects. Of course the experiences of joy are as different as the species differ but all share the desire to procreate (to perserve their power of being in the world). These thought had to wait for development until the work of Charles Dawin two hundred years later.
Spinoza tells us that he wants now to write of emotions that are actively persued by people rather than the passive ones he has been describing so far. By activity Spinoza means the mind's power of thinking, of understanding or reason.