When is marriage permissible and what are its conditions, and when is a child illegitimate or legitimate if a man and a woman secretly agree to marry?

A child is legitimate if the marriage is lawful and the child is not born out of fornication or an invalid marriage known to both spouses to be invalid. A marriage is valid if it fulfills its conditions and pillars, such as offer and acceptance, which do not necessarily have to be in Arabic. In addition, five conditions are required for a valid marriage: the identification of the two spouses, their consent, the presence of a guardian, based on the Prophet’s saying, "There is no marriage without a guardian," and the witnessing of the marriage by two male, legally competent, and just witnesses, and the absence of impediments for both spouses such as difference in religion, kinship, or fosterage.