THE MARRIAGE QUESTION
In the current debates on gay marriage, you can easily get the impression that the only arguments about marriage made before, say, 1970 were based on either religious or natural law traditions. While putting together my online bibliography, I came across this 18th-century essay, from a philosophical point of view I find far more congenial.
AS marriage is an engagement entered into by mutual consent, and has for its end the propagation of the species, it is evident, that it must be susceptible of all the variety of conditions, which consent establishes, provided they be not contrary to this end.
A man, in conjoining himself to a woman, is bound to her according to the terms of his engagement: In begetting children, he is bound, by all the ties of nature and humanity, to provide for their subsistence and education. When he has performed these two parts of duty, no one can reproach him with injustice or injury. And as the terms of his engagement, as well as the methods of subsisting his offspring, may be various, it is mere superstition to imagine, that marriage can be entirely uniform, and will admit only of one mode or form. Did not human laws restrain the natural liberty of men, every particular marriage would be as different as contracts or bargains of any other kind or species.
Taking an emprical approach does not imply endorsing every form of marriage--as those who read the whole essay will discover.
The Library of Economics and Liberty, a.k.a. EconLib, in which this appears is a great online resource, including both current essays and a well-presented full-text library of classic books.