The US council of bishops has a document giving more details: http://www.usccb.org/issues-and-action/marriage-and-family/natural-family-planning/catholic-teachi

The US council of bishops has a document giving more details: http://www.usccb.org/issues-and-action/marriage-and-family/natural-family-planning/catholic-teaching/upload/Unitive-and-Proc-Nature-of-Interc.pdf http://www.usccb.org/issues-and-action/marriage-and-family/n...