As love tends towards the good of the thing beloved, either by taking delight in it if the beloved have it, or in desiring and procuring it for him if he have it not; so it produces hatred, by which it flies the evil which is contrary to the thing beloved, either by desiring and seeking to remove it if it be there, or by keeping it off and preventing its coming if it be not there. But if evil can neither be hindered from approaching, nor be removed, love at least fails not to have it hated and detested. When love therefore is fervent, and is come to that height that it would take away, remove and divert, what is opposite to the thing beloved, it is termed zeal. So that, to describe it properly, zeal is no other thing than love in its ardour, or rather the ardour that is in love. And therefore, such as the love is, such is the zeal, which is its ardour. If the love be good its zeal is good, if the love be bad its zeal is bad. Now when I speak of zeal, I mean to speak of jealousy too: for jealousy is a species of zeal, and if I am not mistaken, there is but this difference between them, that zeal regards the whole good of the thing beloved, with the intention of removing the contrary evil from it, and jealousy regards the particular good of the friendship, that it may repulse all that opposes that.
When therefore we ardently love worldly and temporal things, beauty, honours, riches, rank, -- this zeal, that is the ardour of this love, ends ordinarily in envy: because these base and vile things are so little, limited, particular, finite and imperfect, that being possessed by one, another cannot entirely possess them. So that being communicated to many, each one in particular has a less perfect communication of them. But when, in particular, we ardently love to be beloved, the zeal or ardour of this love turns into jealousy; because human friendship, though otherwise a virtue, has this imperfection by reason of our weakness, that being divided amongst many, each one's part is less. Whereupon our ardour or zeal to be beloved will not permit rivals or companions; and if we imagine we have any, we immediately enter into the passion of jealousy, which indeed in some sort resembles envy, but in reality is very different from it. 1°. Envy is always unjust, but jealousy is sometimes just, if it be moderate: for have not married people good reason to hinder their friendship from being diminished by being shared? 2°. Envy makes us sorry that our neighbour enjoys a greater good than, or a like good with, ourselves; although he is taking from us nothing that we have; and here envy is unreasonable, making us consider our neighbour's good to be our ill. But jealousy is not grieved at our neighbour's having some good provided that it is not our good: for the jealous man does not grieve at his fellow's being beloved by other women so long as he is not loved by the jealous man's wife; indeed, properly speaking, one is not jealous of a rival until one belives that one has gained the friendship of the person loved: if there be any passion before that, it is not jealousy but envy. 3°. We do not presuppose any imperfection in the person we envy, but on the contrary we consider that he has the good which we envy in him: but we presuppose that the person of whom we are jealous is imperfect, fickle, changeable and easily led away. 4°. Jealousy proceeds from love, envy comes from the defect of love. 5°. Jealousy never happens but in matter of love, but envy is extended to all kinds of goods -- honours, favours, beauty. And if at any time one be envious of the affection which is borne to another, it is not for love, but for the fruits that spring from it. The envious man is little troubled to see his fellow in favour with his prince, so that he be not on occasions graced and preferred by him.