The clear yet forgotten truth.
Prescription #1: Give God the greatest possible glory and honor Him with your whole soul.
What is the principle of contradiction? In a nutshell, it’s this: a thing cannot be and not be at the same time. Saint Thomas Aquinas shows that not even God can deny the principle of contradiction.
Regarding the immorality of contraception, Familiaris Consortio explains that "every action which, either in anticipation of the conjugal act, or in its accomplishment, or in the development of its natural consequences, proposes, whether as an end or as a means, to render procreation impossible" is wrong.