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In practice, Chess is not a game of perfect information, since you generally don't know which lines your opponent has prepared beforehand.

sithlord 4y ago
that doesn't matter, you have every bit of information from the board to in theory know every possible outcome. It's not like the opponent can't sneak an extra piece in behind your line. Or randomly turn your rook into their queen...
- charcircuit 4y ago
  >in theory know every possible outcome Does your theory model the maximum possible compute of a player and the amount of time they have to spend computing these outcomes on a turn? People have a finite amount of time to make moves or they lose. Even computers can't explore the full search space. Trivializing the combinatorial explosion of each move is not useful for a chess strategy.
cmeacham98 4y ago
"Perfect information" is a term of art for games, it doesn't literally mean you are omnipotent.
- thom 4y ago
  Is it a particularly useful term here? It seems to mean you could theoretically play perfectly but in almost every real situation you can't, which is true of every human activity (including war). Information is hidden by complexity, but it's still utterly inaccessible.
  - CogitoCogito 4y ago
    You know the entire state of the chess board. You don’t know the entire state of your enemy forces. I’m both cases information could be said to be hidden by complexity, but in the case of war information is also just plain hidden. Edit: it would be similar to your example of war if you e.g. couldn’t see their pieces or something that would cause information asymmetry. This would make the game very different so clearly the term of art _is_ useful and important.
    - thom 4y ago
      I suppose my problem is that the term 'perfect information' doesn't really communicate anything really interesting about chess. Whereas the equally valid term of art 'incomplete information' actually does, because it captures the fact that you lack knowledge of your opponent's strategy, but nobody ever uses that term. Chess is like navigating a maze or a minefield, it's like stumbling into an ambush. It's much more like war than tic-tac-toe.
      - CogitoCogito 4y ago
        > I suppose my problem is that the term 'perfect information' doesn't really communicate anything really interesting about chess. Yes it _does_ communicate something interesting. It is a basic fact about the rules of play. If there were imperfect information, it would be a different game. Poker with perfect information means everyone plays with their cards up. It is a fundamentally different game. The fact that chess has perfect information for all parties is fundamental to the game.
        thom 4y ago
        And while I understand that you’re coming at this from a technical standpoint and I can’t argue with the definition, I still think on a human level chess is more like poker than tic-tac-toe (because you’re spending a lot of time imperfectly filling in gaps in information about what your opponent could be up to), and so the category defined by this technical term isn’t so useful in a human conversation such as we’re having, with no prizes from technical correctness. I’m not really interested in repeatedly restating the definition, I’m saying it’s not a good signifier for the differences between chess and war. Maybe that’s not interesting to you, but it is to me as a player and designer of games! And on a deeper level I suppose I’m guilty of exactly the same thing because this is a thread about poetry anyway. :P
        thom 4y ago
        Eh, no longer really enamoured by these thoughts, because that's really what's interesting about almost any game, but somehow I still bristle whenever people bring this up about chess.
- nanis 4y ago
  Exactly. In particular, "perfect information" means you know all the strategies available to your opponent. You also know that your opponent knows this. And you know that your opponent knows that you know that your opponent knows that you know all the strategies to your opponent ad infinitum symmetrically. In this context, a strategy is a function that maps every history of moves by you and your opponent to an action. So, while chess is theoretically a game of perfect information, in practice it is less so. Real war is not a game of perfect information, because you do not know all the strategies available to your opponent. In addition, you and your opponent's priors may have an intersection of zero measure which makes things very interesting. War is what happens when a certain kind of people try to play the game of chicken which is usually not taught in the kind of fun programs like master's of international studies for members of the preferred party because it is too sophisticated due to the fact that it admits an infinite number of Nash equilibria ... instead, such programs prefer to focus on prisoners' dilemma which, having a dominant strategy equilibrium, is more suitable to ensure such students can go back to the bureaucracy after having passed their classes with perfect As and get us in to war.
mcphage 4y ago
> In practice, Chess is not a game of perfect information, since you generally don't know which lines your opponent has prepared beforehand What do you mean when you say "game of perfect information"? What would be an example of one?
- esafak 4y ago
  https://en.wikipedia.org/wiki/Perfect_information https://en.wikipedia.org/wiki/Perfect_information
  - mcphage 4y ago
    Yes, but according to that definition, Chess is a game of perfect information. So I’m wondering what definition the person I replied to is using, since their claim was that Chess is not a game of perfect information.
arh68 4y ago
There is some truth to this. In theory, chess is a game of perfect information. But in practice, this is only true for ~6-piece endgames: every outcome has been / can be computed. But for any middle- or early-game position, the amount of finite information greatly exceeds any person's or computer's capacity, practically speaking. In concrete terms, the tablebase for 6-piece endgames is ~150 GiB. For 7-piece, it's 16 TiB. [1] https://syzygy-tables.info/ https://syzygy-tables.info/

sithlord 4y ago

that doesn't matter, you have every bit of information from the board to in theory know every possible outcome. It's not like the opponent can't sneak an extra piece in behind your line. Or randomly turn your rook into their queen...

charcircuit 4y ago
>in theory know every possible outcome Does your theory model the maximum possible compute of a player and the amount of time they have to spend computing these outcomes on a turn? People have a finite amount of time to make moves or they lose. Even computers can't explore the full search space. Trivializing the combinatorial explosion of each move is not useful for a chess strategy.

cmeacham98 4y ago

"Perfect information" is a term of art for games, it doesn't literally mean you are omnipotent.

thom 4y ago
Is it a particularly useful term here? It seems to mean you could theoretically play perfectly but in almost every real situation you can't, which is true of every human activity (including war). Information is hidden by complexity, but it's still utterly inaccessible.
- CogitoCogito 4y ago
  You know the entire state of the chess board. You don’t know the entire state of your enemy forces. I’m both cases information could be said to be hidden by complexity, but in the case of war information is also just plain hidden. Edit: it would be similar to your example of war if you e.g. couldn’t see their pieces or something that would cause information asymmetry. This would make the game very different so clearly the term of art _is_ useful and important.
  - thom 4y ago
    I suppose my problem is that the term 'perfect information' doesn't really communicate anything really interesting about chess. Whereas the equally valid term of art 'incomplete information' actually does, because it captures the fact that you lack knowledge of your opponent's strategy, but nobody ever uses that term. Chess is like navigating a maze or a minefield, it's like stumbling into an ambush. It's much more like war than tic-tac-toe.
    - CogitoCogito 4y ago
      > I suppose my problem is that the term 'perfect information' doesn't really communicate anything really interesting about chess. Yes it _does_ communicate something interesting. It is a basic fact about the rules of play. If there were imperfect information, it would be a different game. Poker with perfect information means everyone plays with their cards up. It is a fundamentally different game. The fact that chess has perfect information for all parties is fundamental to the game.
      - thom 4y ago
        And while I understand that you’re coming at this from a technical standpoint and I can’t argue with the definition, I still think on a human level chess is more like poker than tic-tac-toe (because you’re spending a lot of time imperfectly filling in gaps in information about what your opponent could be up to), and so the category defined by this technical term isn’t so useful in a human conversation such as we’re having, with no prizes from technical correctness. I’m not really interested in repeatedly restating the definition, I’m saying it’s not a good signifier for the differences between chess and war. Maybe that’s not interesting to you, but it is to me as a player and designer of games! And on a deeper level I suppose I’m guilty of exactly the same thing because this is a thread about poetry anyway. :P
        thom 4y ago
        Eh, no longer really enamoured by these thoughts, because that's really what's interesting about almost any game, but somehow I still bristle whenever people bring this up about chess.
nanis 4y ago
Exactly. In particular, "perfect information" means you know all the strategies available to your opponent. You also know that your opponent knows this. And you know that your opponent knows that you know that your opponent knows that you know all the strategies to your opponent ad infinitum symmetrically. In this context, a strategy is a function that maps every history of moves by you and your opponent to an action. So, while chess is theoretically a game of perfect information, in practice it is less so. Real war is not a game of perfect information, because you do not know all the strategies available to your opponent. In addition, you and your opponent's priors may have an intersection of zero measure which makes things very interesting. War is what happens when a certain kind of people try to play the game of chicken which is usually not taught in the kind of fun programs like master's of international studies for members of the preferred party because it is too sophisticated due to the fact that it admits an infinite number of Nash equilibria ... instead, such programs prefer to focus on prisoners' dilemma which, having a dominant strategy equilibrium, is more suitable to ensure such students can go back to the bureaucracy after having passed their classes with perfect As and get us in to war.

mcphage 4y ago

> In practice, Chess is not a game of perfect information, since you generally don't know which lines your opponent has prepared beforehand What do you mean when you say "game of perfect information"? What would be an example of one?

esafak 4y ago
https://en.wikipedia.org/wiki/Perfect_information https://en.wikipedia.org/wiki/Perfect_information
- mcphage 4y ago
  Yes, but according to that definition, Chess is a game of perfect information. So I’m wondering what definition the person I replied to is using, since their claim was that Chess is not a game of perfect information.

arh68 4y ago

There is some truth to this. In theory, chess is a game of perfect information. But in practice, this is only true for ~6-piece endgames: every outcome has been / can be computed. But for any middle- or early-game position, the amount of finite information greatly exceeds any person's or computer's capacity, practically speaking. In concrete terms, the tablebase for 6-piece endgames is ~150 GiB. For 7-piece, it's 16 TiB. [1] https://syzygy-tables.info/ https://syzygy-tables.info/