Answers.Body: <p>Disclaimer: this is probably not the answer, but it makes for interesting thinking. </p>
  
  <p>This reminds me of a <a href="https://en.wiktionary.org/wiki/string_bet" rel="noreferrer">string bet</a> in poker. String bets are illegal, because they can be used to gain information – “I’ll see your $5”&hellip;  &lt; watches opponent’s face&gt; "&hellip;  and raise you $20”. </p>
  
  <p>By moving the king first, you are making what would otherwise be an illegal move (moving the king by more than one square) and cannot “string bet”. </p>
  
  <p>If you were to move the rook first, you might observe your opponent’s face, then quickly choose to move the king, claiming that you had intended to castle all along.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-21T14:16:54.020Z
Answers.Text: Welcome to the Chess SE site! You're right in your disclaimer: this would be better posted as a comment on the OP since you are theorising instead of providing a conclusive answer.
Answers.UserDisplayName: Aric
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Answers.CreationDate: 2018-08-21T17:50:17.450Z
Answers.Text: You're answering the question of why you can't move the rook first, but that's not the question that was asked.  And incidentally, it's perfectly legal to pick up your king and hover it like you're going to castle kingside, and then change your mind and castle queenside, so long as you don't let go of the piece.
Answers.UserDisplayName: D M
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Answers.CreationDate: 2018-08-21T18:08:56.087Z
Answers.Text: That "which side am I going to castle to?" trick sounds like a good string bet/fishing for information (+1)
Answers.UserDisplayName: Mawg
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Answers.CreationDate: 2018-08-21T20:23:03.300Z
Answers.Text: This has no value in answering the question. Also, it is not true, as you can pick up and move any piece while observing your oppenent's face, as long as you do not leave the piece in an illegal position.
Answers.UserDisplayName: J. Win.
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Answers.CreationDate: 2018-08-21T20:57:39.047Z
Answers.Text: With a single piece, he knows you are moving a single piece, and can maintaina "poker face". If you move and release arook, he pronbably would not expect you to then "string castle"
Answers.UserDisplayName: Mawg
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-21T21:59:07.373Z
Answers.Text: Opponent-reading doesn't matter in chess, though, since you generally have more to gain from reading the board than from reading your opponent's mind (full information game).
Answers.UserDisplayName: Brilliand
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Answers.CreationDate: 2018-08-22T06:19:00.397Z
Answers.Text: While I agree (and upvoted), in poker we "play the percentages", where ever scrap of information gleaned is a small advantage. No matter how small, over time it can make a difference
Answers.UserDisplayName: Mawg
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-24T14:48:12.420Z
Answers.Text: The equivalent of this seems to be: writing the move down first and showing it to you opponent. I don't know if it is illegal now, but it was fin in 1960s. Here is an example from Fischer-Tal game: "Tal said that 22. Rae1 was the best move. Fischer wrote it down and pushed the scoresheet towards Tal, who grinned. Fischer then played 22. Qc6+ instead. After the game, Tal asked Fischer why he changed his mind and the American said, "Well, you laughed when I wrote it down!"" http://www.chessgames.com/perl/chessgame?gid=1044001
Answers.UserDisplayName: Akavall
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Answers.CreationDate: 2018-08-24T14:52:55.840Z
Answers.Text: "Opponent-reading doesn't matter in chess", of course it is not as important as poker, but it is still important: Here is a video of Kasparov talking about is final game against Karpov in 1985, key part is at 1:17 https://www.youtube.com/watch?v=6vYJyOGKCHE
Answers.UserDisplayName: Akavall
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Answers.CreationDate: 2018-08-27T13:13:08.037Z
Answers.Text: @Brilliand Of course opponent-reading can matter! The board gives you an objective look at the position and best potential moves, but you always have to factor in how your opponent plays too. Nobody makes the best possible move every turn; that's why chess is interesting. I'd play differently against an aggressive or defensive opponent, and if I saw them jump to their pieces after moving my rook, you can sure bet I'd switch to a more conservative move.
Answers.UserDisplayName: Lord Farquaad
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Answers.CreationDate: 2018-08-27T13:18:56.470Z
Answers.Text: @J.Win. Once you touch a piece, you have to move it though, right? Growing up, I was taught that it was for this exact reason.
Answers.UserDisplayName: Lord Farquaad
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Answers.CreationDate: 2021-02-12T03:59:47.200Z
Answers.Text: @Aric i think if the answer was only 1st 2 paragraphs, it would have to be comment instead. with the additional 2 paragraphs, i think it works as an answer.
Answers.UserDisplayName: BCLC
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Answers.CreationDate: 2018-08-21T14:06:05.170Z
Answers.LastActivityDate: 2018-08-21T14:06:05.170Z
Answers.UserDisplayName: Mawg
Answers.Body: <p>I know in general the rules say the hand you move your piece with has to be the one that hits the clock. If you castled with two hands which one would you use to hit the clock? This might be part of the reason for the rule saying you can only castle with 1 hand.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-22T01:22:35.733Z
Answers.Text: I really don't think picking a hand to push a button is that big an issue. We sent men to the moon, I think we can handle this.
Answers.UserDisplayName: Alexander
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Answers.CreationDate: 2018-08-22T04:40:34.573Z
Answers.Text: @Alexander It's more a question of fairness to your opponent. The rule exists to get your hand off the board before hitting the clock so your opponent can make the next move. If you're still moving a piece with your left hand while you hit the clock with your right, you cut into your opponent's time. But the rule is pretty much impossible to follow if you use both hands.
Answers.UserDisplayName: Brian McCutchon
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Answers.CreationDate: 2018-08-22T05:46:41.727Z
Answers.Text: On the other hand, your opponent would know what is happening before you put the second piece down.
Answers.UserDisplayName: PStag
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Answers.CreationDate: 2018-08-22T06:01:03.407Z
Answers.Text: @PStag this assumes it is a legal move. But part of the opponents move is to actually check that. And she can't do that until the pieces are put down. Which might not have happened when the clock is hit when you are using both hands.
Answers.UserDisplayName: Jens Schauder
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Answers.CreationDate: 2018-08-22T10:04:41.360Z
Answers.Text: @BrianMcCutchon: If the reason for the 1-hand rule is to not obstruct the board during opponent's turn, it could easily be replaced with "don't obstruct the board during opponent's turn". And then castling with 2 hands, followed by pressing the clock with either hand while the other is away from the board, would be fine.
Answers.UserDisplayName: Meni Rosenfeld
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Answers.CreationDate: 2018-08-22T16:18:37.407Z
Answers.Text: @Meni That rule would be harder to objectively enforce.
Answers.UserDisplayName: Brian McCutchon
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Answers.CreationDate: 2018-08-23T22:47:44.707Z
Answers.Text: @BrianMcCutchon Your comment is definitely an answer.
Answers.UserDisplayName: jpmc26
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Answers.CreationDate: 2018-08-21T09:27:21.737Z
Answers.LastActivityDate: 2018-08-21T09:27:21.737Z
Answers.UserDisplayName: Hockeyfan19
Answers.Body: <p>Chess rules are all about sequence.  If you use two hands, you don't know which happened first.  So you always use one hand.  First, you make your move, then you hit the clock.</p>
  
  <p>As others have pointed out, the rook move alone could be one or two moves.  Maybe, you were just moving your rook, maybe you were castling.  The King move, however, does determine the one and only move.  There is no other King move that allows the King to move two squares.  By moving the King first, then moving the rook, there are no questions as to the real move.  The Rook, while being part of the move, is forced.  Because this is a sequence, you have to use one hand to play it.</p>
  
  <p>As a side note, if you could use both hands, and you were playing with a clock, you could move the rook and hit the clock with one hand, and move the king with the other hand, and then there would be a sequence argument whether the king had moved before or after the clock hit, and thus whether it was a rook move or a castle.  By requiring one hand to do all three (king, then rook, then clock), there is no question as to what went on.  The king moved two squares first.  That defined the move.  Then the rook moved (with the same hand), then the clock was hit after the board was in a valid situation.  No arguments.</p>
  
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Answers.CreationDate: 2018-08-22T07:20:09.023Z
Answers.Text: +1, I think this is the main reason. One second more or less, once at most, usually doesn't lead to heated rules disputes - but determining whether rook or king was touched first very much does (when using both hands, most people tend to touch the pieces almost simultaneously). This rule exists to make life easier for arbiters.
Answers.UserDisplayName: Annatar
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Answers.CreationDate: 2018-08-21T20:58:39.863Z
Answers.LastActivityDate: 2018-08-21T20:58:39.863Z
Answers.UserDisplayName: Guy Schalnat
Answers.Body: <blockquote>
    <p>why is it illegal to castle with both hands?</p>
  </blockquote>
  
  <p>Because the rules say so.<br>
  From the <a href="https://www.fide.com/fide/handbook.html?id=208&amp;view=article" rel="noreferrer">FIDE Laws of Chess</a> -</p>
  
  <blockquote>
    <p>7.5.4 If a player uses two hands to make a single move (for example in case of castling, capturing or promotion) and pressed the clock, it
    shall be considered and penalized as if an illegal move.</p>
  </blockquote>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2021-02-05T10:40:33.370Z
Answers.Text: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/119361/discussion-on-answer-by-brian-towers-why-is-it-illegal-to-castle-with-both-hands).
Answers.UserDisplayName: Brian Towers
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Answers.CreationDate: 2018-08-21T11:38:06.207Z
Answers.LastActivityDate: 2018-08-21T11:38:06.207Z
Answers.UserDisplayName: Brian Towers
Answers.Body: <p>There is a very important rule for castling with one hand. In the <a href="https://www.fide.com/fide/handbook.html?id=171&amp;view=article" rel="noreferrer">Fide Handbook</a> it is rule 4.1.</p>
  
  <blockquote>
    <p>4.1 Each move must be made with one hand only.</p>
  </blockquote>
  
  <p>The rule applies for all parts of the move, including capturing, castling and promoting.</p>
  
  <p>Now for the reasoning, of why a move needs to be executed with exactly one hand: In case that you are making an invalid move there are specific rules on how to proceed after taking back the invalid move. As a general rule you have to move the first piece that you touched (rule 4.3.a). In case that you use both of your hands for castling, it would be pure luck to say that you need to do another king or rook move. Instead the order is clear. You first touch the king (and move it two squares). Then you touch the rook and move it to the other side of the king.</p>
  
  <p>And why do you have to move the king first? Again it is to reduce any ambiguity. If you'd move the rook next to the king (without touching the king) you already completed a legal move. Castling now would be very weird as for the only time in chess a completed move could still be extended. Your opponent therefore could already make his move and you could still go: "I'm not finished yet, please take back your move". (In an extreme case you could wait for all the time on your clock before announcing that you are castling).</p>
  
  <p>For these reasons it is important that you execute the castling in two steps (first king, then rook). The additional rule that you can only use one hand is not of practical importance as long as both parts of the move are clearly distinguishable. </p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-23T07:39:05.627Z
Answers.Text: pure speculation: (1) "one hand only" minimizes time benefits over handicapped/injured players who can't use 2 hands (2) "one hand only" is a remarkably *simple* rule, and simple rules are easier to teach, follow and arbitrate.
Answers.UserDisplayName: Beni Cherniavsky-Paskin
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Answers.CreationDate: 2018-08-22T08:45:49.910Z
Answers.LastActivityDate: 2018-08-22T11:38:35.390Z
Answers.LastEditDate: 2018-08-22T11:38:35.390Z
Answers.UserDisplayName: QueensKnight
Answers.Body: <p>It would permit a rather interesting ambiguity on the board.</p>
  
  <p>Many have mentioned that the king has to move 2 spaces first, so that there's only one possible valid thing to do.  So let's assume we do this.</p>
  
  <p>With one hand, move the king two spaces.  Once the king is in place (proving you intend to castle), the other hand grabs the rook and moves it.  Meanwhile, the first hand goes to hit the clock.</p>
  
  <p>It is possible that the first hand hits the clock before the rook is moved.  Now you have a really funny situation where your hands are still moving pieces <em>while it is the opponent's turn</em>!  Needless to say, this could be a big deal, especially if the winning move is to take that rook.</p>
  
  <p>To avoid this case, one needs rules which ensure that all pieces are in their final position before the clock is pressed.  Whatever rule FIDE chose, this is the key requirement placed on that rule.  Hands off the board when it's not your turn!</p>
  
  <p>If we use <a href="https://en.wikipedia.org/wiki/%CE%A0-calculus" rel="noreferrer">pi caluclus</a> we can define a process where the clock press must occur after both moves are complete, regardless of which hand does what.  So in theory, one might define a different rule which permits two-handed operation.  However, in real life practical situations, such definitions are unreasonable. They work great with transistors and wires, and less well with human hands.  Instead, we simplify the process by not allowing things to happen in parallel.</p>
  
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Answers.CreationDate: 2018-08-22T00:01:38.480Z
Answers.LastActivityDate: 2018-08-22T00:14:52.287Z
Answers.LastEditDate: 2018-08-22T00:14:52.287Z
Answers.UserDisplayName: Cort Ammon
Answers.Body: <p>In chess, whenever you touch a piece, you MUST move that piece. If you were to begin castling using two hands, and then removed your hands, it would be unclear which piece you would be required to move. This is why it must be done with one hand.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-21T21:29:58.870Z
Answers.Text: If you began castling using two hands, and removed your hands, it's quite clear that you intended to castle -- it's the only permissible two-piece move.
Answers.UserDisplayName: Mark
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-22T08:46:46.390Z
Answers.Text: @Mark that only holds true if you didn't attempt to make an invalid castling move. If the castling is invalid, you still need to decide which piece was touched first.
Answers.UserDisplayName: QueensKnight
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-23T13:55:11.320Z
Answers.Text: @Mark That doesn't matter. Even playing one handed, I could touch my king and then my rook (or vice-versa). You could argue that touching both of those pieces clearly indicates that I want to castle, but that is not what the FIDE rules say: the FIDE rules say that I must move the piece I touched first if I can legally do that. So I'm allowed to touch my king, then touch my rook, then play Ke2. Or touch my rook, then touch my king, then play Rg1. But if I touch my king and rook with different hands at almost the same time, and decide not to castle, can I play Ke2 or Rg1?
Answers.UserDisplayName: David Richerby
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Answers.CreationDate: 2018-08-21T20:39:00.077Z
Answers.LastActivityDate: 2018-08-21T20:39:00.077Z
Answers.UserDisplayName: Hossin
Answers.Body: <p>This is speculation, but I think it's because FIDE wants to reduce the difficulty of knowing whether the rules are followed. One must use the same hand to move the piece and hit the clock because FIDE wants people to not hit the clock before they finish their move, and if different hands were used for the two actions, it could be unclear which happened first. And if someone uses both of their hands for a move, then clearly at least one of the hands used in the move will be different from the one used to hit the clock, making it difficult to see whether the other hand completed its portion of the move before the clock was hit. And it's not just what is easy to see, but what is clearly distinct. If we're trying to decide which hand completed its motion first, that is a matter of perception. But if we're trying to decide whether two hands were used, that's a clear binary. It's easy for two players to have differing opinions as to which hand completed its motion first, but whether two hands were used is an objective fact, and if the players disagree, that strongly suggests that at least one of them is just straight up lying.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2022-11-24T10:29:28.807Z
Answers.Text: +1 for explaining why using both hands to move is in this rule's scope.
Answers.UserDisplayName: Rosie F
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Answers.CreationDate: 2021-01-29T06:28:02.217Z
Answers.LastActivityDate: 2022-11-26T02:44:45.593Z
Answers.LastEditDate: 2022-11-26T02:44:45.593Z
Answers.UserDisplayName: Acccumulation
Answers.Body: <p>Legal is relative. It's illegal in FIDE rules as you can see with other answers.</p>
  <p>But actually it's legal in American rules, at least in USCF rules in 2015. See <a href="https://youtu.be/ge9zoxLoGE4?t=100" rel="nofollow noreferrer">what Hikaru Nakamura said</a> in 2015.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2021-11-05T22:09:02.343Z
Answers.LastActivityDate: 2021-11-05T22:09:02.343Z
Answers.UserDisplayName: BCLC
Answers.Body: <p>I think the reason is a side effect of only being allowed to use one hand to make moves and to hit the clock. Otherwise in mutual time pressure it would be easy to end up making multiple moves when one is only allowed to play one before the opponent gets a go. Multiple hands could more easily support intentional cheating or create situations that an arbiter would find difficult to unwind if summoned</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2021-01-29T04:37:33.533Z
Answers.LastActivityDate: 2021-01-29T04:37:33.533Z
Answers.UserDisplayName: Laska
Answers.Body: <p>The official procedure to castle is (<a href="https://en.wikipedia.org/wiki/Rules_of_chess#CITEREFSchiller2003" rel="noreferrer">Schiller 2003:19–20</a> from Wikipedia):</p>
  
  <blockquote>
    <p>first move the king with one hand and then move the rook with the same hand.</p>
  </blockquote>
  
  <p>By using both hands the player can save time, as would by as using different hands for moving (like promoting a pawn to queen) or moving with a hand and hitting the clock with the other.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-21T15:06:36.373Z
Answers.Text: Very good answer, it appears from your answer that it is about timing and not which hand hits the timer.
Answers.UserDisplayName: Malachi
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-21T16:43:51.087Z
Answers.Text: I'd wager this is for the reason Mawg gave. Moving the king first takes away any option to decide against castling mid-move based on your opponent's reaction. Once the king is released, the only legal move left is to castle.
Answers.UserDisplayName: Lord Farquaad
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-22T06:58:08.467Z
Answers.Text: @LordFarquaad that is indeed a very good reason, but does not explain why you can't do any other moves with both hands (like turning a pawn into a queen) or moving with a hand while the other one is at the clock.
Answers.UserDisplayName: Bernat
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-22T14:00:36.420Z
Answers.Text: @Bernat I think the "jump the clock" rule applies to promoting a pawn, etc.  especially in speed chess, that 1-second time to move your hand from the board tothe clock may matter.
Answers.UserDisplayName: Carl Witthoft
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-22T14:01:34.840Z
Answers.Text: When competing at world class level every millisecond counts.  If over the course of a game one competitor gains half a second of thinking time over the other - in any other sport there'd be a stewards inquiry in how that happened.
Answers.UserDisplayName: Darren Bartrup-Cook
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-08-24T09:56:10.903Z
Answers.Text: Also the risk of ambiguity concerning which piece was touched first, and furthermore that all the pieces have stopped moving before the clock is pressed. E.g. one might otherwise touch the rook first, before realising an error and then grabbing the king with the other hand to change the move into castling.
Answers.UserDisplayName: Robert Frost
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Answers.CreationDate: 2018-08-21T12:56:17.543Z
Answers.LastActivityDate: 2018-08-22T07:00:50.697Z
Answers.LastEditDate: 2018-08-22T07:00:50.697Z
Answers.UserDisplayName: Bernat
Body: <p>I was watching <a href="https://youtu.be/roBJYinLCPc?t=322" rel="noreferrer">the match between Ian Nepomniachtchi vs Hikaru Nakamura</a> and Nakamura used both hands to castle.</p>
  
  <p>Why is it illegal to castle using both hands? What's wrong with that?</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-08-22T08:40:07.033Z
Comments.Text: "What's wrong with that?" Nothing really. One could play chess with two hands, probably, but it would be a slightly different game then.
Comments.UserDisplayName: NoDataDumpNoContribution
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-08-23T17:44:03.977Z
Comments.Text: Very simple: you must play and press the clock with the same hand to ensure you are completing your move before pressing the clock.  If you use two hands to play, you are breaking this rule.
Comments.UserDisplayName: Apollys supports Monica
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-08-23T19:55:54.213Z
Comments.Text: I don't have enough rep to answer but there's a touch-move rule in Chess. If you moved with two hands it would be unclear which piece you touched first. If you touch your Rook first you would have to move your Rook and not be able to castle. Only if you touch your King first and move it two spaces can you castle. Furthermore, once two hands get involved it's not clear that the clock has been hit *after* the move has been made. I had this at the end of a game when an opponent, short on time, moved with one hand and hit the clock with the other. I immediately hit the clock back to his side...
Comments.UserDisplayName: Robert Frost
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-08-23T19:56:15.490Z
Comments.Text: ...and told him to depress it with the hand with which he moved.
Comments.UserDisplayName: Robert Frost
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-08-24T08:08:42.477Z
Comments.Text: @CJDennis I need 10 rep excluding association bonus to answer. I only have 1.
Comments.UserDisplayName: Robert Frost
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-08-24T09:53:36.380Z
Comments.Text: @Trilarion the question asks what is the motivation behind the rule. This is important because there are times when we play chess and may not want to be sticklers for rules.  To do so, it is advantageous to understand what problems might ensue if we relaxed those rules.
Comments.UserDisplayName: Robert Frost
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-08-24T10:44:53.573Z
Comments.Text: @RobertFrost The highest voted answer mentions time saving as potential benefit/problem of castling two-handed. I fully agree that this makes an impact but I wouldn't really call it "something wrong". It's different but not really wrong and one could have asked maybe more neutrally for the implications of doing it two-handed.
Comments.UserDisplayName: NoDataDumpNoContribution
Tags: <rules><castling><illegal-move>
Title: Why is it illegal to castle with both hands?
ThreadText: # Why is it illegal to castle with both hands?
  
  (Asked by: username_0 on 2018-08-21)
  
  I was watching [the match between Ian Nepomniachtchi vs Hikaru Nakamura](https://youtu.be/roBJYinLCPc?t=322) and Nakamura used both hands to castle.
  
  Why is it illegal to castle using both hands? What's wrong with that?
  
  **Tags:** rules, castling, illegal-move
  
  > **Comments:**
  > **username_1**: "What's wrong with that?" Nothing really. One could play chess with two hands, probably, but it would be a slightly different game then.  
  > **username_2**: Very simple: you must play and press the clock with the same hand to ensure you are completing your move before pressing the clock.  If you use two hands to play, you are breaking this rule.  
  > **username_3**: I don't have enough rep to answer but there's a touch-move rule in Chess. If you moved with two hands it would be unclear which piece you touched first. If you touch your Rook first you would have to move your Rook and not be able to castle. Only if you touch your King first and move it two spaces can you castle. Furthermore, once two hands get involved it's not clear that the clock has been hit *after* the move has been made. I had this at the end of a game when an opponent, short on time, moved with one hand and hit the clock with the other. I immediately hit the clock back to his side...  
  > **username_3**: ...and told him to depress it with the hand with which he moved.  
  > **username_3**: @CJDennis I need 10 rep excluding association bonus to answer. I only have 1.  
  > **username_3**: @Trilarion the question asks what is the motivation behind the rule. This is important because there are times when we play chess and may not want to be sticklers for rules.  To do so, it is advantageous to understand what problems might ensue if we relaxed those rules.  
  > **username_1**: @RobertFrost The highest voted answer mentions time saving as potential benefit/problem of castling two-handed. I fully agree that this makes an impact but I wouldn't really call it "something wrong". It's different but not really wrong and one could have asked maybe more neutrally for the implications of doing it two-handed.  
  
  ---
  
  ## 11 answers
  
  ### Answer by username_31 on 2018-08-21. Score: 77 | Accepted answer
  
  The official procedure to castle is ([Schiller 2003:19–20](https://en.wikipedia.org/wiki/Rules_of_chess#CITEREFSchiller2003) from Wikipedia):
  
  > first move the king with one hand and then move the rook with the same hand.
  
  By using both hands the player can save time, as would by as using different hands for moving (like promoting a pawn to queen) or moving with a hand and hitting the clock with the other.
  
  > **Comments:**
  > **username_32**: Very good answer, it appears from your answer that it is about timing and not which hand hits the timer.  
  > **username_10**: I'd wager this is for the reason username_4 gave. Moving the king first takes away any option to decide against castling mid-move based on your opponent's reaction. Once the king is released, the only legal move left is to castle.  
  > **username_31**: @LordFarquaad that is indeed a very good reason, but does not explain why you can't do any other moves with both hands (like turning a pawn into a queen) or moving with a hand while the other one is at the clock.  
  > **username_33**: @username_31 I think the "jump the clock" rule applies to promoting a pawn, etc.  especially in speed chess, that 1-second time to move your hand from the board tothe clock may matter.  
  > **username_34**: When competing at world class level every millisecond counts.  If over the course of a game one competitor gains half a second of thinking time over the other - in any other sport there'd be a stewards inquiry in how that happened.  
  > **username_3**: Also the risk of ambiguity concerning which piece was touched first, and furthermore that all the pieces have stopped moving before the clock is pressed. E.g. one might otherwise touch the rook first, before realising an error and then grabbing the king with the other hand to change the move into castling.  
  
  ---
  
  ### Answer by username_4 on 2018-08-21. Score: 64
  
  Disclaimer: this is probably not the answer, but it makes for interesting thinking.
  
  This reminds me of a [string bet](https://en.wiktionary.org/wiki/string_bet) in poker. String bets are illegal, because they can be used to gain information – “I’ll see your $5”… < watches opponent’s face> "… and raise you $20”.
  
  By moving the king first, you are making what would otherwise be an illegal move (moving the king by more than one square) and cannot “string bet”.
  
  If you were to move the rook first, you might observe your opponent’s face, then quickly choose to move the king, claiming that you had intended to castle all along.
  
  > **Comments:**
  > **username_5**: Welcome to the Chess SE site! You're right in your disclaimer: this would be better posted as a comment on the OP since you are theorising instead of providing a conclusive answer.  
  > **username_6**: You're answering the question of why you can't move the rook first, but that's not the question that was asked.  And incidentally, it's perfectly legal to pick up your king and hover it like you're going to castle kingside, and then change your mind and castle queenside, so long as you don't let go of the piece.  
  > **username_4**: That "which side am I going to castle to?" trick sounds like a good string bet/fishing for information (+1)  
  > **username_7**: This has no value in answering the question. Also, it is not true, as you can pick up and move any piece while observing your oppenent's face, as long as you do not leave the piece in an illegal position.  
  > **username_4**: With a single piece, he knows you are moving a single piece, and can maintaina "poker face". If you move and release arook, he pronbably would not expect you to then "string castle"  
  > **username_8**: Opponent-reading doesn't matter in chess, though, since you generally have more to gain from reading the board than from reading your opponent's mind (full information game).  
  > **username_4**: While I agree (and upvoted), in poker we "play the percentages", where ever scrap of information gleaned is a small advantage. No matter how small, over time it can make a difference  
  > **username_9**: The equivalent of this seems to be: writing the move down first and showing it to you opponent. I don't know if it is illegal now, but it was fin in 1960s. Here is an example from Fischer-Tal game: "Tal said that 22. Rae1 was the best move. Fischer wrote it down and pushed the scoresheet towards Tal, who grinned. Fischer then played 22. Qc6+ instead. After the game, Tal asked Fischer why he changed his mind and the American said, "Well, you laughed when I wrote it down!"" http://www.chessgames.com/perl/chessgame?gid=1044001  
  > **username_9**: "Opponent-reading doesn't matter in chess", of course it is not as important as poker, but it is still important: Here is a video of Kasparov talking about is final game against Karpov in 1985, key part is at 1:17 https://www.youtube.com/watch?v=6vYJyOGKCHE  
  > **username_10**: @username_8 Of course opponent-reading can matter! The board gives you an objective look at the position and best potential moves, but you always have to factor in how your opponent plays too. Nobody makes the best possible move every turn; that's why chess is interesting. I'd play differently against an aggressive or defensive opponent, and if I saw them jump to their pieces after moving my rook, you can sure bet I'd switch to a more conservative move.  
  > **username_10**: @J.Win. Once you touch a piece, you have to move it though, right? Growing up, I was taught that it was for this exact reason.  
  > **username_11**: @username_5 i think if the answer was only 1st 2 paragraphs, it would have to be comment instead. with the additional 2 paragraphs, i think it works as an answer.  
  
  ---
  
  ### Answer by username_12 on 2018-08-21. Score: 34
  
  I know in general the rules say the hand you move your piece with has to be the one that hits the clock. If you castled with two hands which one would you use to hit the clock? This might be part of the reason for the rule saying you can only castle with 1 hand.
  
  > **Comments:**
  > **username_13**: I really don't think picking a hand to push a button is that big an issue. We sent men to the moon, I think we can handle this.  
  > **username_14**: @username_13 It's more a question of fairness to your opponent. The rule exists to get your hand off the board before hitting the clock so your opponent can make the next move. If you're still moving a piece with your left hand while you hit the clock with your right, you cut into your opponent's time. But the rule is pretty much impossible to follow if you use both hands.  
  > **username_15**: On the other hand, your opponent would know what is happening before you put the second piece down.  
  > **username_16**: @username_15 this assumes it is a legal move. But part of the opponents move is to actually check that. And she can't do that until the pieces are put down. Which might not have happened when the clock is hit when you are using both hands.  
  > **username_17**: @BrianMcCutchon: If the reason for the 1-hand rule is to not obstruct the board during opponent's turn, it could easily be replaced with "don't obstruct the board during opponent's turn". And then castling with 2 hands, followed by pressing the clock with either hand while the other is away from the board, would be fine.  
  > **username_14**: @Meni That rule would be harder to objectively enforce.  
  > **username_18**: @BrianMcCutchon Your comment is definitely an answer.  
  
  ---
  
  ### Answer by username_19 on 2018-08-21. Score: 32
  
  Chess rules are all about sequence. If you use two hands, you don't know which happened first. So you always use one hand. First, you make your move, then you hit the clock.
  
  As others have pointed out, the rook move alone could be one or two moves. Maybe, you were just moving your rook, maybe you were castling. The King move, however, does determine the one and only move. There is no other King move that allows the King to move two squares. By moving the King first, then moving the rook, there are no questions as to the real move. The Rook, while being part of the move, is forced. Because this is a sequence, you have to use one hand to play it.
  
  As a side note, if you could use both hands, and you were playing with a clock, you could move the rook and hit the clock with one hand, and move the king with the other hand, and then there would be a sequence argument whether the king had moved before or after the clock hit, and thus whether it was a rook move or a castle. By requiring one hand to do all three (king, then rook, then clock), there is no question as to what went on. The king moved two squares first. That defined the move. Then the rook moved (with the same hand), then the clock was hit after the board was in a valid situation. No arguments.
  
  > **Comments:**
  > **username_20**: +1, I think this is the main reason. One second more or less, once at most, usually doesn't lead to heated rules disputes - but determining whether rook or king was touched first very much does (when using both hands, most people tend to touch the pieces almost simultaneously). This rule exists to make life easier for arbiters.  
  
  ---
  
  ### Answer by username_21 on 2018-08-21. Score: 15
  
  > why is it illegal to castle with both hands?
  
  Because the rules say so.  
  From the [FIDE Laws of Chess](https://www.fide.com/fide/handbook.html?id=208&view=article) -
  
  > 7.5.4 If a player uses two hands to make a single move (for example in case of castling, capturing or promotion) and pressed the clock, it
  > shall be considered and penalized as if an illegal move.
  
  > **Comments:**
  > **username_21**: Comments are not for extended discussion; this conversation has been [moved to chat](https://chat.stackexchange.com/rooms/119361/discussion-on-answer-by-brian-towers-why-is-it-illegal-to-castle-with-both-hands).  
  
  ---
  
  ### Answer by username_22 on 2018-08-22. Score: 11
  
  There is a very important rule for castling with one hand. In the [Fide Handbook](https://www.fide.com/fide/handbook.html?id=171&view=article) it is rule 4.1.
  
  > 4.1 Each move must be made with one hand only.
  
  The rule applies for all parts of the move, including capturing, castling and promoting.
  
  Now for the reasoning, of why a move needs to be executed with exactly one hand: In case that you are making an invalid move there are specific rules on how to proceed after taking back the invalid move. As a general rule you have to move the first piece that you touched (rule 4.3.a). In case that you use both of your hands for castling, it would be pure luck to say that you need to do another king or rook move. Instead the order is clear. You first touch the king (and move it two squares). Then you touch the rook and move it to the other side of the king.
  
  And why do you have to move the king first? Again it is to reduce any ambiguity. If you'd move the rook next to the king (without touching the king) you already completed a legal move. Castling now would be very weird as for the only time in chess a completed move could still be extended. Your opponent therefore could already make his move and you could still go: "I'm not finished yet, please take back your move". (In an extreme case you could wait for all the time on your clock before announcing that you are castling).
  
  For these reasons it is important that you execute the castling in two steps (first king, then rook). The additional rule that you can only use one hand is not of practical importance as long as both parts of the move are clearly distinguishable.
  
  > **Comments:**
  > **username_23**: pure speculation: (1) "one hand only" minimizes time benefits over handicapped/injured players who can't use 2 hands (2) "one hand only" is a remarkably *simple* rule, and simple rules are easier to teach, follow and arbitrate.  
  
  ---
  
  ### Answer by username_24 on 2018-08-22. Score: 6
  
  It would permit a rather interesting ambiguity on the board.
  
  Many have mentioned that the king has to move 2 spaces first, so that there's only one possible valid thing to do. So let's assume we do this.
  
  With one hand, move the king two spaces. Once the king is in place (proving you intend to castle), the other hand grabs the rook and moves it. Meanwhile, the first hand goes to hit the clock.
  
  It is possible that the first hand hits the clock before the rook is moved. Now you have a really funny situation where your hands are still moving pieces *while it is the opponent's turn*! Needless to say, this could be a big deal, especially if the winning move is to take that rook.
  
  To avoid this case, one needs rules which ensure that all pieces are in their final position before the clock is pressed. Whatever rule FIDE chose, this is the key requirement placed on that rule. Hands off the board when it's not your turn!
  
  If we use [pi caluclus](https://en.wikipedia.org/wiki/%CE%A0-calculus) we can define a process where the clock press must occur after both moves are complete, regardless of which hand does what. So in theory, one might define a different rule which permits two-handed operation. However, in real life practical situations, such definitions are unreasonable. They work great with transistors and wires, and less well with human hands. Instead, we simplify the process by not allowing things to happen in parallel.
  
  
  ---
  
  ### Answer by username_25 on 2018-08-21. Score: 3
  
  In chess, whenever you touch a piece, you MUST move that piece. If you were to begin castling using two hands, and then removed your hands, it would be unclear which piece you would be required to move. This is why it must be done with one hand.
  
  > **Comments:**
  > **username_26**: If you began castling using two hands, and removed your hands, it's quite clear that you intended to castle -- it's the only permissible two-piece move.  
  > **username_22**: @username_26 that only holds true if you didn't attempt to make an invalid castling move. If the castling is invalid, you still need to decide which piece was touched first.  
  > **username_27**: @username_26 That doesn't matter. Even playing one handed, I could touch my king and then my rook (or vice-versa). You could argue that touching both of those pieces clearly indicates that I want to castle, but that is not what the FIDE rules say: the FIDE rules say that I must move the piece I touched first if I can legally do that. So I'm allowed to touch my king, then touch my rook, then play Ke2. Or touch my rook, then touch my king, then play Rg1. But if I touch my king and rook with different hands at almost the same time, and decide not to castle, can I play Ke2 or Rg1?  
  
  ---
  
  ### Answer by username_28 on 2021-01-29. Score: 2
  
  This is speculation, but I think it's because FIDE wants to reduce the difficulty of knowing whether the rules are followed. One must use the same hand to move the piece and hit the clock because FIDE wants people to not hit the clock before they finish their move, and if different hands were used for the two actions, it could be unclear which happened first. And if someone uses both of their hands for a move, then clearly at least one of the hands used in the move will be different from the one used to hit the clock, making it difficult to see whether the other hand completed its portion of the move before the clock was hit. And it's not just what is easy to see, but what is clearly distinct. If we're trying to decide which hand completed its motion first, that is a matter of perception. But if we're trying to decide whether two hands were used, that's a clear binary. It's easy for two players to have differing opinions as to which hand completed its motion first, but whether two hands were used is an objective fact, and if the players disagree, that strongly suggests that at least one of them is just straight up lying.
  
  > **Comments:**
  > **username_29**: +1 for explaining why using both hands to move is in this rule's scope.  
  
  ---
  
  ### Answer by username_11 on 2021-11-05. Score: 0
  
  Legal is relative. It's illegal in FIDE rules as you can see with other answers.
  
  But actually it's legal in American rules, at least in USCF rules in 2015. See [what Hikaru Nakamura said](https://youtu.be/ge9zoxLoGE4?t=100) in 2015.
  
  
  ---
  
  ### Answer by username_30 on 2021-01-29. Score: 0
  
  I think the reason is a side effect of only being allowed to use one hand to make moves and to hit the clock. Otherwise in mutual time pressure it would be easy to end up making multiple moves when one is only allowed to play one before the opponent gets a go. Multiple hands could more easily support intentional cheating or create situations that an arbiter would find difficult to unwind if summoned
  
  
  ---
  
  