Marriage God’s Way

What constitutes marriage?  the most common viewpoints:
1) God only considers a man and a woman married when they are legally married—that is, when they become husband and wife in the eyes of the law.
2) A man and a woman are married in God’s eyes when they have completed some kind of formal wedding ceremony solemnized by a third party.
3) God considers a man and a woman to be married at the moment they engage in sexual intercourse.
4) The couple decide to live together, possibly have children, and a certain amount of time passes.