478. The following kinds of intention, though to be recommended, are not necessary for the fulfillment of a law.
(a) It is not necessary, as a rule, that one intend to satisfy one’s obligation, for human lawgivers have not generally the power or the intention to command acts that are purely internal (see 374, 426). Examples: He who hears Mass on a holyday not intending to perform his duty, as he does not know that it is a holyday, has satisfied the law. He who says the rosary out of devotion and then remembers that he has an obligation of saying it because of a promise made or of a penance received, can regard the rosary said as a fulfillment of his obligation.
(b) It is not necessary that one intend that which the lawgiver had in mind as the purpose of the law; for “the end of the law is not a part of the law.” Example: A person who takes only one full meal during Lent, observes the letter of the law; but he misses its spirit if he eats or drinks greedily, daintily or copiously, in order to avoid the mortification intended by the law.
479. If one intends to perform what a law prescribes, but at the same time expressly intends not to satisfy, by that performance, the obligation imposed, one’s act is sufficient or insufficient for fulfillment according to the source from which the obligation arises.
(a) If the obligation arises from the will of the lawgiver, the act is a sufficient fulfillment, since the human lawgiver, as said in the previous paragraph, does not concern himself with what is purely internal. Example: If a person hears Mass on Sunday out of devotion, intending to hear another Mass in satisfaction of the Sunday duty, he is not bound to hear a second Mass, as he has already done all that the law requires.
(b) If the obligation arises from one’s own will, as in the case of a promise or a vow, the act above described is not sufficient fulfillment; for, as the obligation arose from the will, so also the mode of fulfillment is to be determined by the will. Example: One who has vowed to hear Mass, and who now while hearing Mass expressly determines that not this but another Mass will be in satisfaction of his vow, is bound by his vow to hear another Mass.
480. As to virtuous dispositions in fulfilling a law, it is to be observed that, while a good lawgiver always wishes them, he does not always require them as a duty of obedience. The virtuous dispositions referred to are of two kinds: (a) habitual, that is, the permanent spiritual condition of the soul, such as the state of grace, the habit of charity, etc.; (b) actual, that is, the good manner in which the commanded act is done, such as devout attention in hearing Mass, heartfelt contrition in making confession, freedom from vain-glory in fasting, etc.
481. Virtuous dispositions are or are not commanded according as that which is prescribed is or is not a mixed, or a purely external act (see above, 426).
(a) When a mixed act is commanded by law, the virtuous disposition that the nature of the case calls for, but nothing further, is strictly prescribed. Hence, the law of Easter Communion requires that Communion be received in the state of grace, the law of yearly confession that the penitent be truly contrite, the law of Sunday Mass that there be sufficient attention to the Mass; but more perfect dispositions (such as freedom from venial sin in the communicant, perfect contrition in the penitent, the state of grace in him who hears Mass) are not required for the fulfillment of the laws we are considering.
(b) When a purely external thing is commanded, the law does not require internal dispositions, and hence one who performs what is required is not obliged to repeat it on account of the imperfect way he obeyed. Example: He who fasts while he is not in the state of grace is not obliged to fast again to make good what was lacking in his previous disposition.