Norman Chase Gillespie's "three ways in which a normal or ordinary duty may cease to be so because the cost is too high."

1. Moral Cost:

"Sometimes the moral cost of obeying a standard moral rule is too great, so one must make an exception to that rule."

Example: "If the only way to save someone's life is by telling a lie, then one should normally lie."

2. Cost to the Individual:

"[W]hen the cost to the individual of fulfilling that duty is too high," the "ordinary duty may cease to be a duty."

Example: It is morally permissible to crash into another car instead of going off the cliff.

3. Others Aren't Complying

"When virtually everyone else is not doing what ought to be done," and "one person alone cannot accomplish anything," "a normal duty may turn out not to be a duty."

Example: