Conditions:
"So we can summarize the latest and best theological thought on the subject. The Church neither approves nor disapproves of the Rhythm Method as a system to be followed. The Church merely tolerates the use of this method. Tolerates indicates reluctant permission. And the Church only tolerates this method, when three definite factors are present. These three are: First, there is sufficiently serious reason for a given couple to use this method, sufficiently serious enough to justify side-stepping the first purpose of marriage; Second, both husband and wife are truly willing to follow the method —neither one can force the other to adopt this system; Third, the use of this method must not cause mortal sins against chastity nor become a proximate occasion of such sins. The breakdown of any one of those three factors makes the use of Rhythm sinful. So the correct attitude is this: The use of Rhythm is sometimes no sin, sometimes venial sin, sometimes mortal sin. Please stop saying, "Oh, it’s okay, the Church approves it.""