An uncommon prudence is habitual with the subtler depravity, for it has everything to hide.

Melville’s aphorism links moral corruption with a kind of strategic self-control. “Subtler depravity” is not the loud, impulsive vice that exposes itself, but the calculating form that survives by appearing respectable. Such depravity cultivates “uncommon prudence” as a habit—careful speech, measured conduct, and outward propriety—because it must conceal motives, past actions, or ongoing schemes. The line suggests that prudence, usually praised as a virtue, can be weaponized: discretion and restraint may signal not integrity but the need to maintain a façade. It is a warning about mistaking polished caution for goodness, and about how evil can thrive through social camouflage.