You can only use NFP for grave reasons...What are these reasons?

Pope Pius XII Who Gave Us
 the Four "Grave Reasons"

The last post about the sinfulness of contraception and sterilization (Read: 6 Reasons Why Contraception is Sinful) stirred up some comments about natural family planning (NFP). NFP is a popular contemporary term for "periodic continence." NFP works by observing the cycles of a wife's fertility and then avoiding the nuptial embrace during her times of fertility so as to avoid pregnancy. In NFP, the husband and wife abstain from the nuptial embrace altogether during the time of the wife's monthly fertility.

The Church allows married couples to practice periodic continence only for grave or serious reasons. These reasons were explicitly listed by Pope Pius XII in his “Address to the Italian Catholic Union of Midwives" from 1951.

NFP or periodic continence can only lawfully be practiced without sin for grave reasons, which he lists as “medical, eugenic, economic, and social” reasons.

If a couple is healthy, financially secure, and living in a stable community, then recourse to NFP is contrary to the mind of the Christ's Church and sinful.

Note that NFP or "periodic continence" in itself is morally neutral since observing a woman's cycle and remaining continent are morally neutral. Therefore, NFP is not intrinsically evil. Artificial contraception (condoms, the pill, interuptus) are intrinsically evil because they directly intervene in the natural process. Artificial contraception obstructs the natural act either through devices, chemicals, or direction intervention.

So then, NFP can be used when there is a proper "grave"or "serious" circumstance, and the Holy Father provides four such circumstances. Let's go through these four grave reasons.

continue at Canterbury Tales