Talk:Perfect information

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"Complete does not imply perfect information; but if background as "moves by nature," perfect implies complete information." - from Is this true? I guess "moves by nature" here must refer to the assignment of types/payoff functions to participants(?)--Frank Guerin 18:09, 8 May 2005 (UTC)

Nature's move is the assignment of types to players (and their type determines their payoff function). In describing a game of incomplete information, one might treat it as if it were a game of perfect information since nature has revealed some actions to some players that it hasn't revealed to others (i.e their types), so players do not know the entire game history. This is due largely to work by John Harsanyi. He wrote a paper in 1967 called "Games with incomplete information played by Bayesian players". Treborbassett 08:08, 9 May 2005 (UTC)

Shouldn't this be merged with complete information? The definition given is exactly the same.

The entry on complete information is misleading (at best). This should definately be fixed at some point (maybe I'll do it soon). Complete information means I know who the other players are and what the payoffs to their possible action are to them, but during the game I may not know what action they took (perhaps they made a choice in secret). Perfect information games are ones where at any given time I know what the other players did, there are no secrets. thanks for pointing this out, its a real problem! --Kzollman June 28, 2005 23:49 (UTC)

Why does a Google search and an internal link for "imperfect information" lead to "perfect information," yet this article doesn't even mention it? I would argue that the difference (at least as far as game theory is involved) isn't just merely semantic. Should it have its own internal link or should a part be added to this article, or neither? Collin Imhof 03:44, 3 April 2006 (UTC)


.'that perfect information does not exist in marker' or 'in society'.. Dunno.. As analyzing games, it can obviously exist... that sentence seems as always it won't exist... Althrough at the begining it says about chess.. It looked odd, I think... 19:59, 31 March 2007 (UTC)

I removed those two paragraphs, thanks for pointing them out. They sounded suspiciously like original research. If the original author can find a citation for these, then we can put them back in. Although, I suspect the wording would needed to be changed. --best, kevin [kzollman][talk] 20:42, 31 March 2007 (UTC)

German wiki & merge[edit]

Hi there!
in German wikipedia we have de:Spiel_mit_vollständiger_Information which means "Game with complete information" complete game. However, the link links to "perfect information" - not complete information.
Also, Solved_game is in german just a part of de:Gewinnstrategie.
However, there are only few links. I'd recommend to merge some of the articles into one, like perfect & complete information articles into somethink similar game theory, so we can link each other more easily.
Additionaly, there is (in german): de:Gewinnstrategie (meaning winning strategy).
Ok, I got a bit confused. Any suggestions?
--Bmhm 18:56, 19 July 2007 (UTC)

Bmhm - Thank you for your comments, finding out how other languages do things can often offer new perspectives. Unfortunately, things here are a bit complicated. Complete game is, in fact, a term used in the sport baseball, and this term is not often used in English publications about game theory. I was previously unaware of Solved game, I will need to take a look at it. We had considered merging complete and perfect information into a single article. These refer to different concepts, but the English terminology introduces more confusion than it solves. To be honest, I don't remember what we decided about the merge. With regards to winning strategy, the only thing we have is a section in Determinacy about it, see Determinacy#Winning_strategies. --best, kevin [kzollman][talk] 19:54, 19 July 2007 (UTC)

perfect or imperfect information?[edit]

I feel confused our participation behavior from game theory perspective. In wikipedia or even other online communities, we may write down something after we read others' posts. Is it perfect information? Only next time we visit the same page, we can know what others respond to our posts. From this perspective, it seems that we don't know how others respond when we act. So it should be a simultaneous move. In this sense, the information is imperfect. I really feel confused about this question. who can answer it?SimonSun 07:54, 14 November 2007 (UTC)

Definition incomplete?[edit]

"In game therory, a game is said to have perfect information if all players know all moves that have taken place." This statement does not make sense without it being possible to have games with perfect and imperfect information at the same time. I am not an expert in game theory but this would appear to be a clear contradiction. In a card game, all of the previous moves are known to all players while they don't know the location of the other cards. I know that the term is used differently by different communities but this definition seems incomplete. Tetron76 (talk) 17:49, 9 September 2010 (UTC)

In a card game, if you know that another player has "played" a card but you don't know exactly which card was played (for example if you only see the back of the card), then it is not considered as "knowing all moves". But I agree that we should also know the current "location" of the cards for it to be perfect information. I'll try to update the page to incorporate that fact. 7804j (talk) 23:56, 16 June 2016 (UTC)


  • The first link is a commenter quoting Wikipedia, not Wikipedia copy/pasting material.
  • The second uses the phrase "Chess is an example of a game with perfect information (...)" but I'd argue that there isn't much copyrightable about this phrase-- there aren't any other ways to put it. Both sentences depart from that phrase in different directions; I think their similarity is just coincidence. -M.Nelson (talk) 18:03, 27 November 2010 (UTC)

Split: Game Theory vs. Microeconomics.[edit]

These are different notions and should have separate pages. — Preceding unsigned comment added by NoWikiFeedbackLoops (talkcontribs) 20:24, 22 May 2012 (UTC)

Perfect Information in "Game theory" section[edit]

Now the first section reads thus:

Game theory In game theory, an extensive-form game has perfect information if each player, when making any decision, is perfectly informed of all the events that have previously occurred. [1]

Chess is an example of a game with perfect information as each player can see all of the pieces on the board at all times. Other examples of perfect games include Tic-tac-toe, Irensei, and Go. The formal definition can be easily extended to include games with exogenous uncertainty from chance events, such as in Backgammon, or simultaneous move games, such as in the iterated prisoners' dilemma, or both, such as in Goofspiel.

Card games where each player's cards are hidden from other players are examples of games with imperfect information.[2][3]

So the first paragraph talks about extensive-form type games.

The second paragraph is also talking about extensive-form type games.

But the third paragraph flips to a card game which is a normal-form game. Card games are a large subset of Normal-form games.

It seems that paragraphs 1 and 3 are mixing apples and oranges.


I think paragraph 1 should be over game theory as a whole.

Then paragraph 2 about extensive-form games. (yada yada. Chess is an example of an ...)

Paragraph 3 about normal form games. (yada yada. Card games are typical examples of normal form games...)

--- also it isn't clear in sentence about backgammon as to what is being extended. The definition of "perfect information" or the definition of an "extensive-form" game. If the definition of "perfect information" is being extended, how? what are the implications?

In general the whole aspect of randomness vs perfect information in this just isn't clear.

— Preceding unsigned comment added by Um297zoa (talkcontribs) 23:33, 3 June 2014 (UTC)