Blood Relationship as Impediment

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

Degrees of consanguinity are distinguished according to lines. 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 called lateral or collateral lines (brother, sister, first cousins, second cousins, and so on).

Consanguinity is, by natural law, an impediment to marriage between certain closely related persons. It would be contrary to the ends of marriage, chief of which is the welfare of offspring, if inbreeding were practiced. What was necessary in the beginning 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 marriage is forbidden.