474. The internal acts concerned in the fulfillment of a law are: (a) those in the intellect, such as knowledge; (b) those in the will, such as consent, motive.
475. Knowledge of what one is doing is sometimes necessary, sometimes unnecessary for the fulfillment of a law.
(a) If the law is prohibitive, knowledge is not necessary, since nothing more is required by the law than the omission of what is forbidden. Example: He who ate no meat on a day of abstinence has fulfilled the law, even though he was unconscious all day.
(b) If the law is preceptive of a payment to be made, knowledge is not necessary, since the law requires nothing more than the effect of an external act. Example: He who pays his taxes while intoxicated fulfills his obligation, even though he does not know what he is doing.
(c) If the law is preceptive of an act to be performed, knowledge is required, for it is supposed that the act will be exercised in a human manner. Example: He who sleeps all during Mass on Sunday does not fulfill his duty, for the law intends that one assist at Mass in a human way (i.e., with consciousness of what is being done).
476. Fulfillment of a law is not morally good and meritorious, unless it is voluntary (see 97 sqq.); but the legal obligation is sometimes satisfied even by an unwilling fulfillment.
(a) When the law commands a payment to be made, one may will the contrary of what is commanded and yet fulfill one’s obligation. Example: He who pays his taxes unwillingly and under compulsion satisfies the law, which requires not an act, but its effect.
(b) When the law forbids something, it is possible that one does not will the omission commanded and yet fulfills one’s obligation. Example: He who intends to eat meat on a day of abstinence which he thinks is a meat day, but, being unable to find what he wants, omits the meat, satisfies the law, which requires only that one omit what is forbidden and have no will to violate the law.
(c) When the law commands that an act be performed, one must perform the act willingly, since the law being for humans intends that fulfillment be made in a human manner. Examples: He who is dragged to church and forcibly detained there during Mass, does not satisfy the law of sanctifying the Sunday, since force makes his assistance at Mass involuntary (see 52). A child that goes to church only to escape punishment satisfies its duty, if, in spite of reluctance, it really intends to hear Mass, for fear does not necessarily make an act involuntary (see 41 sqq.).
477. As to the intention required in fulfilling a law, it is to be noted that one must have, at least implicitly, the intention of doing what the law prescribes, in the case given in the third section (c) of the preceding paragraph. Example: He who goes to church on Sunday while Mass is being said with no other purpose than that of hearing the music or of waiting for a friend, does not satisfy the Sunday duty, since he does not at all intend to hear Mass.