1. Absolute Incapacity or Prohibition: arises from:
a) Consanguinity means blood relationship and bars a man from marrying:
- His mother or grandmother how highsoever,
- His daughter or grand-daughter how lowsoever,
- His sister whether full, consanguine or uterine,
- His niece or great niece how lowsoever,
- His aunt (fathers sister, mothers sister) or great aunt, how highsoever, whether paternal or maternal A marriage with a woman prohibited by reason of consanguinity is void. Issues from such marriage are illegitimate.
b) Affinity prohibits a man from marrying:
- His wife's mother or grand-mother how highsoever
- His wife's daughter or grand-daughter how lowsoever
- Wife of his father or paternal grand-father how highsoever
- Wife of his son or son's son or daughter's son how lowsoever A marriage with a woman prohibited by reason of affinity is void.
c) Fosterage means when a woman other than its own mother has suckled a child under the age of two years, the woman becomes the foster-mother of the child. A man may not, for instance, marry his foster-mother or her daughter, or his foster sister.
Under the Sunni law, there are a few exceptions to the general rule of prohibition on the ground of fosterage and a valid marriage may be contracted with:
- Sister's foster mother, or
- Foster's sisters mother, or
- Foster's sons sister, or
- Foster brother's sister.
The Shia jurists place fosterage and consanguinity on the same footing and refuse to recognize the exception permitted by the Sunnis. The above mentioned prohibitions on account of 'consanguinity', 'affinity' or 'Fosterage' are absolute and the marriages contracted in contravention of these rules are void.