A Formula Without the Fine Print

Take the rule that whoever loves less holds the power. Picture two people: one moved to the partner’s country, gave up work, barely speaks the local language and spent several years looking after children; the other kept an income, a flat, a profession and a social circle. In a break-up both may suffer emotionally, but the material consequences will differ. The folk formula notices the asymmetry, yet it is still unclear which variable it measures: the strength of feeling, the cost of exit, the outside alternative, or all of these at once. While the variables stay mixed, it is easy to derive from the observation the advice to love less and keep your distance. Separate them, and instead of advice to be colder a different question appears: what is the dependency made of, and can its design be changed? The move itself is what matters: work out what world would have to exist for the formula to be true.

A model is useful when it forces you to name the participants, their goals, the information available, the possible actions and the consequences of each decision. Without that it is easy to hide the desired answer inside the calculation. You can stipulate in advance that men seek many partners and women seek one reliable one, and then obtain those same preferences after several pages of mathematics. The calculation will be flawless and will tell you roughly as much as a mirror does.

A substantive model leaves the outcome open. It compares the behaviour of participants with identical goals but different costs of pregnancy, and checks how the choice changes with reliable contraception, the right to inherit, an income of one’s own and a different family structure. That is how a stable preference gets separated from a strategy that is sensible under specific constraints. Talk of “man’s nature” and “woman’s nature” then breaks down into testable parameters of risk, rights, income and technology. This is less impressive than a reference to cave-dwelling ancestors, but it does distinguish an explanation from a literary genre.