Thus the passions … follow from this same necessity and efficacy of nature; they answer to certain definite causes … possess certain properties as worthy of being known … the contemplation in itself affords us delight. I shall, therefore, treat of the nature and strength of the emotions according to the same method, as I employed heretofore in my investigations concerning God and the mind. I shall consider human actions and desires in exactly the same manner, as though I were concerned with lines, planes, and solids.
– Spinoza, Ethics