This issue has been thrashed out many times, and never gets anywhere. Instead, everyone keeps reiterating the same points over and over in different ways and becoming more entrenched in their individual views, often without fully understanding the position of those with differing views. I don't want to have such a debate again. Instead, I would like us to all work together to carefully define each position and to have every point explained clearly, once, and in a place that is easy for people to find. Then anyone can refer to these threads as a resource and use them as the basis for their own research, or for writing a document on the topic.
To structure this clearly, I have started several threads, each with a specific purpose.
0) This thread is for general discussion, keep debate to a minimum but if it must happen it goes here. If in doubt, post here. This is the primary discussion thread.
Then I have three additional threads that exist simply to collate the scriptural evidence supporting each position. No discussion of other positions is to occur in those threads. Each should ultimately have each point made once, comprehensively but efficiently, so they are quick to read while carefully elaborating the position. To achieve this, I will delete any posts that stray off-topic, and may do some trimming if some points become too repetitive.
I see four basic answers to "When does marriage begin?", and I have a thread for each position.
1)
Sex forms a marriage (if you have sex you are married by default, unless you were ineligible to marry)
2)
Covenant forms a marriage (marriage is formed by contract / agreement / covenant / consent, sex may then occur within marriage)
3)
Possession / Either forms a marriage (if you have a woman and nobody else objects, she's your wife)
4)
Both form a marriage (only once you have a covenant, and have consummated it with sex, are you married).
If there are any other basic positions that should be added to this list, tell me here. If one of these needs to be redefined, tell me also. I'm not structuring this discussion to achieve a particular outcome, I have no agenda here. I'm structuring it simply in an attempt to actually be able to address the topic without dissolving into yet another back-and-forth debate that goes nowhere.
Past threads on this topic for reference (and to see the previous arguments this topic has caused!):
What constitutes marriage?
Profane Relationships
Genesis 2:24
Concubines... just a bit of mental jousting
Sex, marriage & emotions - ramblings of a FW
Related, could be useful:
Language affects our ability to think
One flesh