I'd like to define "purchasing" as picking up something and walking out of the store without paying. Unfortunately, for practically all of civilized history, the definition has been giving something in return.
So, when people start talking about gay people demanding the marriages they're due, I wonder when the concept of "marriage" was redefined. Then I remember this is about benefits, insurance, and estates, not love and marriage. Then I start wondering again if I can fight for the redefinition of "purchase"...