The “reserving” of some clause within one's own mind which makes one's expressed statement true. It arises out of conflicts between the obligation to tell the truth and the obligation to keep a secret. A politician facing an embarrassing question may reply, “I don't know”; his mental reservation is “in my capacity as a private citizen.” The doctrine of mental reservation is found in Roman Catholic moral theology, which holds that lying is always and necessarily sinful. A lie is the intentional assertion of what is contrary to a man's inward thought. It is also an offense against justice, truth being a debt which we owe to others. Roman Catholic teaching has distinguished two types of mental reservation. Strict mental reservation involves the speaker's mentally adding some qualification to what he has said so that the sense is different and the hearer deceived. Wide mental reservation, on the other hand, arises from the permitted ambiguity of the words or the circumstances in which they are spoken. Strict mental reservation was condemned byin 1679. Wide mental reservations, however, are not lies, provided there is a good reason. In this case the speaker is permitting the hearer to remain in his misunderstanding of words susceptible to a different interpretation.