What makes a marriage?

Catholic teaching says:

Consent — and the maturity and mental capacity to be able to fully consent

Intention for lifelong fidelity

Openness to new life.

So, my question to non-Catholic readers is, what do you think the (secular) definition of marriage is?

I’m not talking about what makes a marriage successful.  I’m speaking more narrowly:  under what circumstances would you say, “that’s only a sham marriage”?

Conducting a marriage ceremony to enable someone to stay in the country, with no intention to have any relationship?

“Marrying” a business partner because it makes legal arrangements work better?

Marrying in order to qualify for financial aid as an independent student?

Marrying with no intention of permanence, or even no desire for permanence, or even a stated intention to part ways after a given length of time or a change in circumstances?

Marrying with no intention of “for richer or for poorer, in sickness and in health” — with the intention, indeed, to leave should the other party experience hardship, or, say, become pregnant?

Marrying with no intention of mutual support — “you manage your own affairs, and I manage mine, and we divide the common expenses 50/50, tough luck if you can’t afford it”?

Marrying while hiding some significant fact from the future spouse (an ongoing affair, a secret child, criminal activity, etc.), that, if known, would have led the spouse to cancel the wedding?

Or would you say, “any marriage that’s recognized by the government is always by definition a ‘valid marriage’ and any further debates are just about whether you cast moral judgement on the spouses”?

Image:  By Jeff Belmonte from Cuiabá, Brazil (Flickr) [CC BY 2.0 (http://creativecommons.org/licenses/by/2.0)], via Wikimedia Commons