Contribution and the agreed rule: two more claims on one word

Effort and prior agreement are both called fair, and they routinely collide.

Shares by contribution says the person who put in more should get more out. It is the fairness of the shared garden bed: whoever did the watering has the strongest claim on the tomatoes. Its appeal is that it responds to something people actually did rather than something they merely are, and it rewards effort in a way the other definitions do not. Its weakness is measurement. Contribution has visible forms, such as hours of digging, and invisible forms, such as the person who noticed the plants needed staking and quietly bought the stakes.

Shares by an agreed rule works entirely differently. It says the answer was settled in advance, so the current merits do not need to be assessed at all. Four housemates draw lots for bedrooms on the day they move in, and the person who drew the small room lives with it. The strength here is finality. Nobody has to relitigate the allocation every month, and the mental cost of that peace is genuinely large. Agreed rules are how groups avoid spending their whole shared life in negotiation about things that are, in the end, quite small.

The collision is predictable. Six months later the person in the small room is working from home and the person in the large room is barely there. Need and contribution both now point one way; the agreed rule points the other. Whoever benefits from the draw will say a deal is a deal, and they are describing a real principle, not merely defending their interest. Whoever lost it will say circumstances changed, and they are also describing a real principle. Both statements are true. Only one of them can determine who sleeps where, and no amount of sincerity decides which.