A person, who indulges himself in any pleasure, while his friend lies under affliction, feels the reflected uneasiness from his friend more sensibly by a comparison with the original pleasure, which he himself enjoys.

This contrast, indeed, ought also to inliven the present pleasure.

But as grief is here supposed to be the predominant passion, every addition falls to that side, and is swallowed up in it, without operating in the least upon the contrary affection.

It is the same case with those penances, which men inflict on themselves for their past sins and failings.

When a criminal reflects on the punishment he deserves, the idea of it is magnifyed by a comparison with his present ease and satisfaction; which forces him, in a manner, to seek uneasiness, in order to avoid so disagreeable a contrast.
This reasoning will account for the origin of envy as well as of malice.
The only difference betwixt these passions lies in this, that envy is excited by some present enjoyment of another, which by comparison diminishes our idea of our own: Whereas malice is the unprovoked desire of producing evil to another, in order to reap a pleasure from the comparison.