A virtue allied to veracity (see truthfulness), and indeed an integral part of that virtue, whose function it is to incline a person to the fulfillment of his promises. Whereas veracity inclines one to conform his speech to the judgment of his mind, fidelity disposes him to conform his deeds to his promissory commitments. The notion of fidelity is thus intimately associated with that of a promise, and the obligations of fidelity differ according to the different senses in which the term promise can be understood.
When a promise is contractual, i.e., when it has the force of a contract or a quasi-contract, it gives rise to an obligation in commutative justice. This obligation is a grave one and, where matters of importance are concerned, cannot be violated without serious sin. Thus, for example, conjugal fidelity and the promised payment of debts voluntarily contracted are grave obligations in conscience.
But when moral theologians refer to fidelity in its narrowest and most specific sense they do not have in mind the fidelity that obliges in virtue of commutative justice but are concerned rather with fidelity in the fulfillment of promises of a noncontractual kind, that is, with promises made spontaneously and out of pure liberality, and with no view to benefits received or expected. The obligations of fidelity understood in this sense bind less urgently than those arising from commutative justice, and their deliberate violation would not ordinarily involve grave sin.
However, it is not always easy to distinguish a simple promise binding only in fidelity from a gratuitous, unilateral contract that binds in commutative justice. The intention of the party making the promise is decisive in most cases, but in some circumstances the nature of what is promised, and the trouble and expense to which the promisee may be put by reason of his expectations, indicate that the promisor intends (or at least should intend) to bind himself seriously.
Bibliography: thomas aquinas, Summa theologiae, 2a2ae, 110.3 ad 5; 89.7; 98.3 ad 1 and 3. b. h. merkelbach, Summa theologiae moralis, 3 v. (Paris 1949) 2:497–500.
[p. k. meagher]
fi·del·i·ty / fəˈdelətē/ • n. faithfulness to a person, cause, or belief, demonstrated by continuing loyalty and support. ∎ sexual faithfulness to a spouse or partner. ∎ the degree of exactness with which something is copied or reproduced: the 1949 recording provides reasonable fidelity.