Blood Relationship as Impediment

Blood relationship or consanguinity isestablished by natural descent from a common ancestor.

Degrees of consanguinity are distinguished according tolines. The ascending and descending line (father, son,grandson, great-grandson) is the direct line. The lines onthe various levels of the ascending and descending line are calledlateral or collateral lines (brother, sister, firstcousins, second cousins, and so on).

Consanguinity is, by natural law, an impediment tomarriage between certain closely related persons. It would becontrary to the ends of marriage, chief of which is the welfare ofoffspring, if inbreeding were practiced. What was necessary in thebeginning of the race is not needed now. The voice of nature, aswell as the voice of human experience, proclaims the unlawfulnessof marriage between near relatives.

The Church, by her disciplinary or regulative laws(canons), fixes the degrees of consanguinity within which marriageis forbidden.