1. About the Idea of the Name ‘Satisfaction’ Taken Generally

11. About the first point, one needs to note that the idea of satisfaction taken generally is this: satisfaction is the voluntary giving back of the equivalent of that which is otherwise not due.

12. The first point, namely ‘giving back’, is plain, because it is not an absolute gift; for the term ‘satis-’ [‘enough’] states commensuration with something correspondent that precedes.

13. As to the term ‘voluntary etc.’, this is plain, because if the giving back were involuntary it would not be ‘satis-faction’ [‘doing enough’] but ‘satis-passion’ [‘suffering enough’], and in this way he from whom the penalty due for a fault committed is unwillingly exacted suffers enough but does not do enough (= ‘satisfy’).

14. As to the term ‘equivalent etc.’, this is plain because the verbal element ‘satis-’ implies this; justice also requires this, giving satisfaction back for that which it corresponds to.

15. The fourth part, namely ‘otherwise not due’, is plain, because if it were otherwise due, satisfaction would not be made for it, for there would not be correspondence in justice with it but with something else.

16. And this idea of satisfaction applies to any contract and obligation whatever. For in this way can he who receives a benefit make satisfaction to the benefactor, and in this way can he who is loved to the lover, by recompensing equal love. And thus can this idea be found both in free acts of the will and in acts in any way necessary, namely contracts, where there is a sort of obligation necessitating the making of a return. Likewise, since guilt makes the delinquent a debtor to him against whom he sins, this idea of satisfaction can be found there, namely that he should return to him what is equivalent and otherwise not due, up to the amount he took away by sin.