“It's like when we used to let kings take over from their fathers: that's the craziest rule that ever existed. If the king dies they let his kid be the king - what are the odds that he's not going to be a piece of shit? That's one of the weirdest things that we've ever done as a race of people.” - Louis C.K.
I’ll confess I wasn’t that excited when it was announced they’re finally getting round to ending male primogeniture for the monarchy. While it’s good in principle in the sense that it’s absurd and sexist to say that a second-born son is going to be a better ruler than a first-born daughter, it’s also a bit absurd to say the first-born is inherently going to be better at the job than the second-born. After a bit more thought though, I realised that if you look at it from the other direction (who it keeps off the throne) it actually makes a lot of sense as a method of reducing violent political conflict.
If we imagine a different situation where an out-going king chose one of their children on the basis of temperament and competency, this would for many years introduce uncertainty about who the next king would be. Uncertainty raises the potential power of factions as they angle behind various contenders which in turn increases the probability of violence. By introducing criteria for a ‘good king’ it would also make it more likely that outsiders would try to make a case that they better fulfil the criteria than any of the heirs on offer, which again, increases the likelihood of violence. Always sticking with the first-born means you don't have to judge on any other criteria, and the order of succession will change as few times as possible[1. To bring this back to male primogeniture, because swapping heirs from a girl to a boy increases the number of order changes, on the face of it it's a bad thing - but if the fundamental concern is stability and there's a substantial faction that would back a male heir over a female heir anyway, there's nothing to be gained by a system that legitimized another potential faction.]. So looking at it this way it isn’t about selecting the right ruler, it’s about establishing norms that disqualify everyone else. Lots of people can raise an army but almost no one is the first-born son of the king.
All this was going through my head about about the same time as I was reading the Song of Ice and Fire books, which was convenient because Martin spends an a lot of time dwelling on the problems of succession. While the series is often quite politically interesting what I hadn’t noticed straight-off is how methodical he is at taking apart and examining the problem of what makes a monarch legitimate - each of the various Kings that end up fighting over the Iron Throne in Game of Thrones and Clash of Kings are operating on different principles of legitimation. Because Robert and Ned have overthrown Aeron the norms governing succession have broken down and the stage is set for people who would ordinarily be disqualified to make a play for the throne. Given Joffrey is illegitimate, Stannis’ claim as the younger brother of ex-King Robert is fairly straight-forward but there is no way for Renly to trace a claim that doesn’t involve going through Stannis first. Instead Renly bases his claim on a charismatic populism, not that he is the rightful heir but that he would be a better and more popular king than everyone else is on offer. Elsewhere Robb Stark is effectively making the case for a right of national self-determination for the North, Joffrey’s claim is mostly already being on the throne (there’s a lot to be said for institutional inertia) and when the Greyjoys start making trouble, they claim their lands by right of conquest - something that lurks in the background of everyone else’s claims is their ability to enforce them (the throne they’re competing over is literally made of swords after all).
It’s worth noting that not all of these are incompatible (there’s no particular reason why Renly’s populism needs to clash with Robb’s national self-determination) but between them all they lack a common denominator to settle the issue other than endless bloody war, that’s exactly what happened. While saying primogeniture results in peace would clearly be an overstatement, it definitely has its upside. It’s also inherently unstable because of the original problem that, just as it doesn’t have a mechanism for selecting the most fit king, it also doesn’t have a method of weeding out unfit ones either - for each generation debilitating mental illness is a roll of the dice, as is the possibility that the new monarch might just be such an awful person that they threaten the system. It’s not wonderful, but part of what makes Westeros such a depressing place is that sometimes it might just be as good as you're going to get.