2. Relative Incapacity or Prohibition:
Springs from cases which render the marriage invalid only so long as the cause which creates the bar exist. The moment it is removed, the incapacity ends and the marriage become valid and binding. The following are the cases:
Polygamy, or marrying a fifth wife.
Absence of proper witnesses
Differences of religion
Woman undergoing IDDAT
Unlawful conjunction: means contemporaneously marrying two women so related to each other by consanguinity, affinity or fosterage, which they could not have lawfully intermarried with each other if they had been of different sexes. Thus a Muslim cannot marry two sisters, or an aunt and her niece.
Under the Shia Law, a Muslim may marry his wife's aunt, but he cannot marry his wife's niece without her permission. Marriage prohibited by reason of unlawful conjunction is void under Shia Law.
Polygamy or marrying a fifth wife: means plurality of wives, i.e. marrying a fifth wife. It is unlawful for a Mohammedan to have more wives than four.
A Muslim woman cannot marry more than one husband. If a woman marries a second husband, she is liable for bigamy under Sec.494, Indian Penal Code and the issues of such a marriage are illegitimate.
Absence of proper witnesses: It is essential amongst the Sunnis that at least two male witnesses or one male or two female witnesses must be present to testify that the contract was properly entered into between the parties. The witnesses must be of sound mind, adult and Muslim.
In Shia Law, a marriage contracted by the spouses themselves or their guardians in private are held valid. Presence of witnesses is not necessary.
Differences of religion: A Sunni male can marry a Muslim female (Of any sect) or a Kitabia. Marriage with the Kitabia, i.e. a woman who believes in a revealed religion possessing a Divine Book viz Islam, Christianity and Judaism is valid under the Sunni Law. But he cannot marry an idolatress or a fire-worshiper. A marriage, however with a idolatress or a fire worshiper is merely irregular in Sunni Law, but void in Shia Law. A Muslim woman cannot marry any man who is not a Muslim, whether he is Kitabia (i.e. man believing in a revealed religion possessing a divine book) or not . According to Mulla, a marriage between a Muslim woman and Non-Muslim male is irregular. But according to Fyzee, such a marriage is totally void
Under Shia Law, no Muslim, whether male or female can marry a non-Muslim in the Nikah form.
Thus a marriage between a Muslim and a non-Muslim can only take place under The Special Marriage Act, 1954.
Woman undergoing Iddat: Iddat is a period during which it is incumbent upon a woman, whose marriage has been dissolved by divorce or death of her husband to remain in seclusion and to abstain from marrying another husband
Under Sunni Law marriage with a woman undergoing Iddat is irregular and not void. But under Shia law marriage with a woman who is undergoing Iddat is void.