The consent of a woman is given through her guardian while a man directly gives his consent by himself. So the contract of marriage is made between the guardian and the future husband. The guardian could be a particular or general guardian. The general guardian is a court judge where the woman has no guardian who is a blood relative. Particular guardians are either the father, in leau of him a brother who attained majority or an uncle from the side of her father.
Abu Hanafi has not accepted a representation of a woman by a guardian unless the woman is a young, an insane i.e. disabled for whatever reasons. Whether the consent is given directly by the woman or through her guardian it should not be defective. Any factor that has the power to influence and affect the normal functioning of the human mind can become a cause for defective consent.
Jurists divide the causes into two kinds: natural causes [samawiyah] and acquired causes [mukeasabah]. Now we will, briefly, discuss both and their further classification