Captain Logic and the Polygamy Argument

Some people, who I will charitably describe as “offensively moronic”, keep claiming that legalising same-sex marriage will lead to polygamy.

Two things before we go further. First, a note on terminology; when most people use the word “polygamy” they mean “polygyny” (one husband, multiple wives), but the term “polygamy” does cover all the combinations (polygyny, polyandry, and group marriage).

Second, there’s a limit to the discussion; I am not making a judgement, one way or another, about whether or not polygamy is OK, desirable, or if the “social/legal equality” argument requires polygamy to be legalised as well. Those are beyond the scope of discussion; they are irrelevant. I am dealing with a specific claim.

This claim is;

legalisation of same-sex marriage will lead to the legalisation of polygamy.

There are two important things to note;

  1. The inevitability of polygamy; the claim is nearly always worded so as to present the legalisation of polygamy as an inevitable, unavoidable, consequence of the legalising same-sex marriage; and
  2. This is a positive claim; it is proposing that something will occur. It is not saying something won’t happen or doesn’t exist; it is asserting that something will happen or does exist – that x will lead to or result in y.

Let’s explore this, shall we?

That argument is horseshit (a technical term meaning that the argument “is groundless and baseless, lacking any factual supporting evidence”).

Look at the map of nations that recognise or permit polygamy, and compare it with the nations that recognise same-sex marriage. The United Kingdom and South Africa are the only two crossovers; the former recognises polygamous unions created abroad where they are already legal for welfare purposes, and the latter recognises them in customary law. In South Africa, the customary law recognition predates same-sex marriage recognition in that country – and the civil law prohibits it. The nations that do recognise polygamy (my research indicates it’s polygyny – group marriage and polyandry aren’t legal anywhere in the world) do not recognise same-sex marriage – in fact they are usually nations extremely intolerant of homosexuals. Even South Africa is patchy there.

That’s all she wrote.

There is no evidence whatsoever that legalising same-sex marriage will lead to legalising polygamy. If anything, the opposite is true; there is evidence of a strong correlation between the legal recognition of polygamy and anti-gay laws – but remember that correlation is not causation.

The argument is horseshit. But it still gets used, often with “you can’t prove it won’t!” – enter Captain Logic, stage left.

Because that’s where it falls down; reversing the burden of proof by demanding that I demonstrate that same-sex marriage won’t lead to polygamy. But if you’re making a positive claim, it’s up to you to demonstrate its truthfulness or accuracy. You have to show evidence for it. It is not up to your opponent to prove a negative. To reverse the burden of proof is to commit a logical fallacy on par with an ad hominem (where you attack my character, not my argument).

On closer examination, the argument bears the hallmarks of a slippery slope, an appeal to fear, and an appeal to consequence. It states x will lead to y without showing how (and against the evidence), and it tries to invalidate x through appeal to fear of y, without showing why y should be feared.

The same-sex-leads-to-polygamy argument’s logic is false on multiple levels, and it’s not even remotely true.

Things could change in the future, but for now it is completely invalid.

If you use the polygamy argument, you fail logic forever; shut up, the adults are talking.