Thus the passions of hatred, anger, envy, and so on, considered in themselves, follow from this same necessity and efficacy of nature; they answer to certain definite causes, through which they are understood, and possess certain properties as worthy of being known as the properties of anything else, whereof 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.
DEFINITIONS I.

By an adequate cause, I mean a cause through which its effect can be clearly and distinctly perceived.

By an inadequate or partial cause, I mean a cause through which, by itself, its effect cannot be understood.
II.