Contraception separates the unitive from the procreative aspects of the marital act…every marital act must be open to life and unitive.
(it is not the fact that NFP is “natural” as opposed to artificle that is key here…that is just the “name” that stuck…really it is “periodic continence”)
There are a lot of articles out there that will fill this out…search the main Catholic Answers site put "contraception"in the key word…and NFP.
catholic.com/ And Janet Smith has a number of articles such as “Contraception why not?”
and here are some from CUF
cuf.org/faithfacts/details_view.asp?ffID=24
NFP can help one conceive or if the couple has a serious reason…to wait.
Here is a “terse” overview
From the Compendium of the Cathechism --issued by Pope Benedict XVI
- What is the meaning of the conjugal act?
2362-2367
The conjugal act has a twofold meaning: unitive (the mutual self-giving of the spouses) and procreative (an openness to the transmission of life). No one may break the inseparable connection which God has established between these two meanings of the conjugal act by excluding one or the other of them.
- When is it moral to regulate births?
2368-2369
2399
The regulation of births, which is an aspect of responsible fatherhood and motherhood, is objectively morally acceptable when it is pursued by the spouses without external pressure; when it is practiced not out of selfishness but for serious reasons; and with methods that conform to the objective criteria of morality, that is, periodic continence and use of the infertile periods.
- What are immoral means of birth control?
2370-2372
Every action - for example, direct sterilization or contraception - is intrinsically immoral which (either in anticipation of the conjugal act, in its accomplishment or in the development of its natural consequences) proposes, as an end or as a means, to hinder procreation.
vatican.va/archive/compendium_ccc/documents/archive_2005_compendium-ccc_en.html