Marriage usually involves sharing and exchanging a huge bunch of things. Love, sex, childcare, money, cooperation in finding a mutually agreeable place for the knives to live, etc. For all of these but one, you can verify whether I’m upholding my side of the deal. And for all but one, I can meaningfully promise to keep my side of the deal more than a day into the future. Yet the odd one out, love, is the one that we find most suited to making eternal promises about. Are these things related?