Most fairness arguments are two definitions wearing the same word.

Fair means at least four different things in ordinary life, and the four often point in opposite directions. Naming the one you are using will end more arguments than winning them.

Four people finish a meal and the bill arrives. One says split it evenly. One says pay for what you ordered. One says the person who is between jobs should pay less. One says we agreed at the start that whoever booked the table pays, so that settles it. Nobody at that table is being difficult. Each of them is applying a rule that is genuinely a rule of fairness, and each rule has a long history of ordinary use. The trouble is not that three of them are wrong. The trouble is that the word fair is being asked to carry four separate jobs at once, and it cannot.

Call the four by their plain names. Equal shares: everyone gets the same amount. Shares by need: the person who needs more gets more. Shares by contribution: the person who put in more takes out more. Shares by an agreed rule: whatever we settled in advance is what happens, regardless of the other three. Every one of these is described as fair by people using the word in good faith. In many situations they happen to agree, which is why the conflict stays hidden most of the time. When they diverge, the argument starts, and it usually starts without either party noticing that the disagreement is about vocabulary.

Watch what happens next in the restaurant. The even splitter thinks the itemiser is being petty. The itemiser thinks the even splitter is helping themselves to a subsidy. The one who mentioned the person between jobs feels the other two are cold. The one who invokes the booking agreement feels ignored. Each reads the others as motivated by self interest, because from inside a single definition the other definitions look like excuses. This is the most common failure in everyday fairness disputes: a difference in definition gets misread as a difference in character, and the argument moves from the bill to the people, where it cannot be settled at all.

Test it yourself with a smaller case. Two flatmates share one good parking space under a carport. Equal shares says alternate weeks. Need says the one who starts work at four in the morning should have it. Contribution says the one who paid to resurface the driveway should have it. An agreed rule says the arrangement made when they moved in stands, even if circumstances have since changed. Ask which is fair and you will get a confident answer from anyone you ask, and you will get different confident answers from different people. The confidence is real. The disagreement is real. Neither is evidence of bad faith.

Our position is narrow and we will hold to it across everything we publish. We do not think one of the four is the true meaning and the others are impostors. We have not found an argument that settles that, and we are suspicious of anyone who says they have, because the settled answer always turns out to be the one that suits the person offering it. What we do think is that most disputes are resolvable at a lower level than the deep question. They are resolvable by saying out loud which definition you are working from, and asking the other person the same, before anyone starts defending a position.

That sounds too simple to be useful. In practice it is startlingly effective, because it changes what the conversation is about. Instead of trading accusations of stinginess and greed, two people are comparing two rules, and rules can be compared calmly. Often one party will simply concede: yes, in this case need matters more than the arrangement we made, because the arrangement was made before anything changed. That concession is almost impossible while the argument is about who is being unreasonable, and it is quite easy once the argument is about which of four ordinary meanings applies to a shared carport on a Tuesday.