Prediction markets
The title is not the contract
A prediction-market title invites a quick answer. The settlement rule decides which answer gets paid.
“Will the city have a white Christmas?”
I can picture the argument already. Someone posts a photograph of snow outside their window. Someone else posts a photograph of rain across town. Both think the prediction-market contract is obvious.
For this article, the market is fictional. Let its rule say that Yes pays only if the official weather station at City Airport records at least one centimetre of snow on the ground at noon on 25 December, local time. A snowy park at 11 a.m. would not settle it. A flurry with no snow on the ground would not settle it. Neither would a beautiful photograph with no location or timestamp.
The small print is the big question
Polymarket's clarification guide says a market's title describes it, while its rules determine how it resolves. Those rules specify a resolution source, an end date and edge cases. Its resolution guide says winning shares receive $1 and losing shares become worthless when a market is finalized under its rules.
The gap between title and rule is not a trick exclusive to one venue. It is a general reading problem: everyday language compresses details, and a settlement mechanism needs those details. “Snow,” “release,” “mention,” “launch,” “by Friday” and “official” can all hide a question about source, time zone, threshold, or who decides.
For my fictional Christmas market, I would save four fields before I saved a forecast:
- Station.
- Threshold.
- Timestamp.
- Resolution source.
A beautiful snow photo is not one of them.
That makes the rule necessary to interpret the price. Two people can disagree about the likely outcome because they are picturing different events. A trader who researched the airport station while everyone else watched downtown photographs may appear to have a forecasting edge. Perhaps they only read the contract more carefully. Those are different stories, and the second is useful without pretending it predicts the weather.
What happens when wording changes?
Polymarket also says that when it clarifies a market, resting orders are cancelled and the order book is cleared. That detail matters because a clarification can change what a participant thinks they are offering to buy or sell. I would not write that a specific market “changed the rules” without its dated rule history and clarification record; an update to wording, a correction, and a disputed settlement need separate evidence.
The fictional white-Christmas example gives me a practical habit. Before I think about a probability, I want to be able to finish this sentence: Yes pays if this source reports this condition at this time. If I cannot, the big percentage can wait.