According to the Madras High Court if a couple indulges in premarital sex it will be considered marriage!
This judgement was given because of a couple who had not married but had two children. In order to make the man pay a monthly maintenance of Rs 500 to the woman, this judgement had to be passed where in a couple who lives together and has kids should be considered a "married" couple.
But this does not mean that just because a couple have sex before marriage that they are automatically married! By that logic more than half the population of this country are married! Do you agree?