I don´t want to claim authorship of this idea, but, since, It is my rendering of it , I will just mention that I got it from Pruss, in some sense, though it could be the case that the way i am presenting it is not faithful or correct, so, it shouldn´t be taken as good, on the basis of Pruss´s purported support.
Now, any thoughts , questions, objections? I will be happy to engage with.
Marriage as a kind of relationship is both normatively and non-normatively explanatory.
P1. Inductive reasoning about marriage is appropriate.
P2. There are genuine similarities between marriages,
Especially if we focus normatively and cull outliers (e.i. green card marriage. child marriage.), when, narrowing the field is important in science.
P3. Explanations (normative and non-normative) on the basis of marriage are genuine explanations.
Cm: So, plausibly, marriage is a natural kind.
Reference:
natural-kinds-types-relationships-as-token-processes
natural-kinds-an-example
Which kind of marriage is a natural kind?
Marriage in which the woman is subordinate? I which the man is? Marriage in which both partners have equal rights? Marriage without the intent to procreate?
What are those 'genuine similarities between marriages'? A same -sex marriage, e.g. has a genuine similarity to another marriage in that it is based on love and mutual respect and in that it is between two partners and does not involve more partners, etc.
A marriage between a man and a woman past the age of feritily is genuinely similar to some same-sex marriages in that there is no intent to procreate.
Another problem is that is marriage is a natural kind, then is celibacy a natural kind as well?
What if marriage between a man and a woman is a natural kind for heterosexual people while same-sex relations and marriage is a natural kind for homosexual people?