XXIII. On Restitution from Unjust Profit

What sort of obligation of restitution is had from unjust profit? Resp. An obligation of restitution is had first from the fact that someone has been unjustly made richer from another's thing. This head of restitution, from the fact that someone has been unjustly made richer from another's thing, does not regard another's thing itself, but profit made from another's thing and fruits received from another's thing; and not any fruits whatever, but fruits immediately received from another's thing, by which someone has been unjustly made richer, as we have already explained. Cf. 1341. But concerning restitution of profit and fruits of this kind we have already said enough. Cf. XXII. Wherefore nothing remains to be added here. Moreover, the obligation of restitution by reason of unjust profit is had in every contract in which someone does not preserve due equality; and restitution then must also be made from another cause, namely from the cause of contract, concerning which it will have to be spoken below. But this must be noted: that as another's thing is a source of restitution, so from the fact that someone has been unjustly made richer there is another source of restitution; for restitution must then be made not of another's thing itself, but of the profit unjustly made, as can be seen, e.g., in a mandatary, borrower, depositary, mutuum by reason of usury, acceptance of what was not owed, etc.