(b) One is excused when a lower or less urgent law is in conflict with a law that is higher or more urgent. In such a case the greater obligation prevails, and the lesser obligation disappears. Examples: The divine laws that one must preserve one’s life or administer Baptism to a dying person prevail over the human law of attendance at church. The less urgent law of fasting yields to the more urgent law of devoting oneself to duties required by one’s state of life, if there is a conflict between the two laws. 495. The loss, evil or inconvenience that constitutes moral impossibility with respect to a law, must bear a proportion to the law itself; and hence the higher or the more imperative the law, the greater must be the reason that suffices to excuse from it. 496. Only a learned and prudent man can determine whether moral impossibility exists with reference to a particular case, and hence it would be dangerous for those who are not theologians to decide, either for themselves or for others. The points that have to be considered in judging are: (a) whether or not the difficulty is of a gravity proportionate to the importance of the law (e.g., a graver reason is required to excuse from a law that obliges under mortal sin than to excuse from a law that binds under light sin); (b) whether or not the difficulty is grave in relation to the person concerned (e.g., an obligation that is easy for a healthy person may be very difficult for one who is infirm). 497. It is never lawful to bring about either physical or moral impossibility of observing a law, if this be done with the sole or principal purpose of escaping one’s duty. Example: To go away on Saturday in order to avoid Mass on Sunday. 498. It is lawful to cause impossibility of observing a law, if there be some sufficient reason for doing this; for it is lawful to do something from which two effects, one good and the other bad, result, if the good effect is the one intended, and there is a sufficient reason for permitting the evil effect (102 sqq.). Example: It is sometimes lawful to do some extra work that is very useful, even if the labor makes one unable to observe a fast. 499. The sufficient reason spoken of in the last paragraph is one that is proportionate to the urgency and importance of the command and to the frequency of the non-observance. Examples: A greater reason is required to take up some work which will make it impossible to keep the fast, if this be done on the fast day itself, than if it be done the day before. A far greater reason is required to take up some work that makes the observance of the fast impossible, if this happens frequently or habitually, than if it happens only once or twice. 500. Cessation of Law.--A law ceases in two ways.