What's the Law of Surprise exactly?

Question

What's the Law of Surprise exactly?

It is mentioned several times in the series with Paveta and Durry or Geralt and Ciri but it can't seem to have any good explanation of what is this Law.

Answer 1

The Law of Surprise, as presented in the witcher's universe, seems to be an informal rule/promise/oath used when repaying a debt. A person may choose to grant another person the right to take something that belongs to the indebted person, that they're not aware of yet. Granted, in most cases it's not supposed to be a child or half a kingdom, but something smaller: maybe the year's harvest yields more crops than expected, or something like that. Here's an explanation from "The Last Wish", the short story, narrated by the druid Mousesack:

Indeed, Urcheon of Erlenwald made a strange request of King Roegner, a strange reward to demand when the king offered him his wish. But let us not pretend we’ve never heard of such requests, of the Law of Surprise, as old as humanity itself. Of the price a man who saves another can demand, of the granting of a seemingly impossible wish. “You will give me the first thing that comes to greet you.” It might be a dog, you’ll say, a halberdier at the gate, even a mother-in-law impatient to holler at her son-in-law when he returns home. Or: “You’ll give me what you find at home yet don’t expect.” After a long journey, honourable gentlemen, and an unexpected return, this could be a lover in the wife’s bed. But sometimes it’s a child. A child marked out by destiny.

There's a bit of an observer's bias that we have here: all the examples at hand somehow involve Ciri, i.e. a prodigal child, "marked by destiny". In reality, I imagine it would've been used by common folk when there were no other means to repay a person, and it would involve much simpler things.

Geralt himself does not believe in the Law of Surprise:

"Geralt?"

"Yes, Calanthe?"

"You do not believe in destiny?"

"I don't know if I believe in anything. As for destiny... I think that it is not enough. There must be something more."

"I must ask you a question on this point: what was your story? It is said that you were a child-surprise. Mousesack said..."

"No, Calanthe. Mousesack had something else in mind. Mousesack undoubtedly knows... but he resorts to legend when it suits him. I was never the thing that one does not expect to find on his return. It is wrong to say that I became a witcher for that reason. I was an ordinary orphan, Calanthe, a kid that his mother, whom he does not remember, did not want. But I know who she is."

The queen was all ears, but Geralt did not continue.

"Are all the stories about the law of surprise also legends?"

"All of them. How can one know whether something is chance or destiny?"

I imagine the only reason he's invoked it is because he wouldn't have wanted to be paid in coin, and maybe it seemed like a smart joke to him. Universe, however, seems to get the last laugh over Geralt more often than not.