The definition of marriage is always changing

The argument

The argument proceeds by showing that marriage has no fixed definition to defend. In the past, our definition and understanding of marriage included polygamy, and some of the societies that shudder at the idea of taking multiple spouses today once saw nothing wrong with it. What changed was not a discovery about what marriage essentially is but the attitudes of the people doing the defining. Interracial marriage makes the same point within living memory. At one time interracial marriages were abhorrent and even illegal, and that prohibition was defended in its day as a protection of marriage rather than as an attack on it. Few hold that belief today. The institution did not collapse when the restriction was lifted; the definition simply widened, and the earlier boundary now looks like a prejudice that had been written into the law rather than a feature of marriage itself. What both cases establish is that our definition of marriage evolves and changes with public opinion. This is the ordinary history of the institution rather than a series of exceptions to it, and it matters because the objection to extending marriage usually rests on the opposite assumption, that there is a settled meaning being departed from. If the meaning has never been settled, that objection has nothing to stand on, and each past boundary was defended in much the same terms now used against the current one. The conclusion follows from the pattern. Attitudes to homosexuality have changed in the way attitudes to interracial marriage changed, and the definition has always tracked such shifts. It makes sense that as attitudes to homosexuality change, so too should our definition of marriage, and that gay marriage should be legalized.

Context

Marriage has never been a fixed concept. Allowing same-sex marriage is a natural evolution of the concept.

Premises

Counter-arguments

Our definition of marriage can only be expanded when public attitudes force it to expand. This is not happening everywhere. There are many countries where public attitudes remain obstinately opposed to gay marriage and same-sex couples. Until societal currents force the definition to expand, the existing definition of marriage between one man and one woman must prevail.

Rejecting the premises

[Rejecting P2] Public attitudes have not necessarily warmed to gay marriage.