Answers.Body: <p>Here are a couple of relevant questions and answers that might help to explain why the bishop move happens:</p>
  
  <ul>
  <li><a href="https://chess.stackexchange.com/questions/4733/morphy-defence-in-ruy-lopez/4734#4734">Morphy Defence in Ruy Lopez</a></li>
  <li><a href="https://chess.stackexchange.com/questions/226/why-is-the-ruy-lopez-such-a-common-opening">Why is the Ruy Lopez such a common opening?</a></li>
  </ul>
  
  <p>In summary the main points seem to be that:</p>
  
  <ul>
  <li><p>Black loses as much time chasing the bishop as White does retreating it</p></li>
  <li><p>White can gain a long-term advantage from Black's weaker Queen side pawn structure</p></li>
  </ul>
  
  <p>As you might expect in such a popular opening though it's very finely balanced for both sides.</p>
  
  <p>If as you say you are <em>not</em> seeing a6 and b5 in the games you're looking at, you might be looking at games where Black plays the Berlin Defence: 3... Nf6. This is quite popular at the moment in very high level games. </p>
  
  <p>If you want to see some games where the pawn move a6 is played, "putting the question to the bishop", here's a link: <a href="http://www.chessgames.com/perl/chessopening?eco=C70" rel="nofollow noreferrer">http://www.chessgames.com/perl/chessopening?eco=C70</a></p>
  
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Answers.UserDisplayName: EastNine
Answers.Body: <p>The moves Bg5 and Bb5 usually have one the following six purposes:</p>
  
  <ol>
  <li>To pin a knight on f6/c6</li>
  <li>To <em>provoke</em> ...h6 or ...a6, weakening the pawns</li>
  <li>To trade White's bishop for its counterpart (usually because the position later will make Black's bishop a better piece than White's)</li>
  <li>To take the knight in order to break up the pawns behind it</li>
  <li>To take the knight because it defends a central square White wants to occupy with a piece, usually his own knight</li>
  <li>To set up the removal of the knight and prepare a mate at h7 once the knight defender is eliminated</li>
  </ol>
  
  <p>If Black responds with ...h6 (say), White can maintain the pin with Bh4.  On the kingside, Black is left with a difficult choice: kick the bishop away with ...g5, weakening the kingside, or leave it there as a loose piece.</p>
  
  <p>White often intends to transfer the bishop to the diagonal h2-b8 anyway, when Black's punting the bishop only wastes a tempo and weakens his kingside.</p>
  
  <p>The same is true about the possible destinations of the bishop on the queenside. On the a2-g8 diagonal, it hits the f7 square, which is usually uncomfortable for Black in the KP openings (and obviously good for White).</p>
  
  <p>In some openings, White wants to exchange the bishop, with or without the knight already on f6/c6. In the Sicilian Defense, Rossolimo Attack, White plays 3.Bg5 in reply to 2...Nc6, but Black hasn't moved the d-pawn, so there's no pin. Black doesn't normally play ...a6, because he's not feeling any pain from the Bishop (yet).</p>
  
  <p>In the Canal-Sokolsky Nimzovitch Variation of the Sicilian (also known as the Moscow, although there is a completely different <em>Prins Moscow</em> Variation), the line runs like this:</p>
  
  <pre><code>[FEN ""]
  [Event "B51"]
  [White "Sicilian Defence"]
  [Black "Canal-Sokolsky Nimzovich"]
  [Result "*"]
  [ECO "B51"]
  
  1. e4 c5 2. Nf3 d6 3. Bb5+ {What?? No knight to pin?} Bd7 4. Bxd7+ Qxd7 5. O-O (5. c4) *
  </code></pre>
  
  <p>...there's no knight there; White just wants to get rid of Black's good bishop, and saddle Black with a bad one unless he either fianchettoes it on the kingside, or moves all of those pawns (ain't gonna happen). So he invites it to interpose, and trades it off. </p>
  
  <p>In the French Defense, the Alekhine-Chatard attack (strictly speaking, the <em>Albin</em>-Alekhine-Chatard), White leaves the bishop on g5 and props it up with his own h-pawn, daring Black to take it. If Black does, he ends up staring down the barrel of White's king's rook on an open file:</p>
  
  <pre><code>[FEN ""]
  [Event "C13"]
  [White "French Defence"]
  [Black "Albin-Alekhine-Chatard Attack"]
  [ECO "C13"]
  
  1. e4 e6 2. d4 d5 3. Nc3 Nf6 4. Bg5 Be7 5. e5 Nfd7 6. h4 *
  </code></pre>
  
  <p>Black doesn't play ...h6 here, since there's no point; White will just take on the bishop e7.</p>
  
  <p>In the Ruy Lopez, in 75% of games Black plays 3...a6 immediately. He has no concerns about weakening his queenside; in fact, the pawn storm it initiates often constitutes his main counterplay.</p>
  
  <p>So, these are some illustrations of what the bishop is doing there, and when it may not make sense to chase it.</p>
  
  <p><em>Note: Many of these ideas are also present in variations with colors reversed, i.e. ...Bg4 and ...Bb4. The latter is the primary theme of the Nimzo-Indian and Bogo-Indian Defenses.</em></p>
  
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Answers.UserDisplayName: jaxter
Answers.Body: <p>"Spanish Bishop" can become very useful and strong piece, especially when it arrives on the c2 square sometimes.</p>
  
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Answers.Text: This answer is too vague in my opinion. Could be more concrete?
Answers.UserDisplayName: lodebari
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Answers.UserDisplayName: Keshav
Body: <p>Oftentimes a bishop will move to b5 or g5 early in the game.</p>
  
  <p><a href="https://i.sstatic.net/4R8sa.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/4R8sa.png" alt="enter image description here"></a></p>
  
  <p>I personally never do this because I see a6 coming, and if I move the bishop back to a4, then b5, nearly trapping the bishop, and certainly having made it a waste of time to move it to b5 in the first place.</p>
  
  <p>However, when I watch games by top-level players, bishops get moved to the 5 row all the time, and nobody ever fights them away with pawns like I think they will. Why not?</p>
  
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2016-09-22T08:01:35.157Z
Comments.Text: Can you give an example?
Comments.UserDisplayName: SmallChess
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2016-09-22T18:51:30.197Z
Comments.Text: A bishop is placed there most of the time to threaten the opponent in some way. The position in the diagram is very unlikely to come from a high level game, as that bishop has absolutely no business on b5. And if that is the case, you're right. But if there is a purpose(like in the Ruy, hitting a defender of e5, or relocating the bishop to a good diagonal while weakening black's queenside pawns), the move shouldn't be discarded for some loose reasoning, like it "nearly" getting trapped. Chess is not a game where inprecise reasoning works all the time.
Comments.UserDisplayName: Scounged
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2016-09-23T08:45:28.613Z
Comments.Text: Each position is different, you cannot try to generalize this move amongst different opening positions. In the exact position you showed it is a bad move; but after 2. Nf3 Nc6, it is a good move.
Comments.UserDisplayName: M.M
Comments.ContentLicense: CC BY-SA 3.0
Comments.CreationDate: 2016-09-24T00:33:44.677Z
Comments.Text: After a while you can learn when a piece is really at risk of getting trapped. In double king pawn openings you can often play c3 or d3, useful moves supporting the center, and the light squared bishop is safe, while Black's queenside moves may just open up holes in his position. They aren't as serious as if he moved pawns on the kingside in front of a castled king, but they add up.
  
  Still, getting a bishop nearly trapped can look tricky and worrisome.
Comments.UserDisplayName: aschultz
Tags: <strategy>
Title: Why not fight off a bishop on row 5 with pawns?
ThreadText: # Why not fight off a bishop on row 5 with pawns?
  
  (Asked by: username_0 on 2016-09-22)
  
  Oftentimes a bishop will move to b5 or g5 early in the game.
  
  [![enter image description here](https://i.sstatic.net/4R8sa.png)](https://i.sstatic.net/4R8sa.png)
  
  I personally never do this because I see a6 coming, and if I move the bishop back to a4, then b5, nearly trapping the bishop, and certainly having made it a waste of time to move it to b5 in the first place.
  
  However, when I watch games by top-level players, bishops get moved to the 5 row all the time, and nobody ever fights them away with pawns like I think they will. Why not?
  
  **Tags:** strategy
  
  > **Comments:**
  > **username_1**: Can you give an example?  
  > **username_2**: A bishop is placed there most of the time to threaten the opponent in some way. The position in the diagram is very unlikely to come from a high level game, as that bishop has absolutely no business on b5. And if that is the case, you're right. But if there is a purpose(like in the Ruy, hitting a defender of e5, or relocating the bishop to a good diagonal while weakening black's queenside pawns), the move shouldn't be discarded for some loose reasoning, like it "nearly" getting trapped. Chess is not a game where inprecise reasoning works all the time.  
  > **username_3**: Each position is different, you cannot try to generalize this move amongst different opening positions. In the exact position you showed it is a bad move; but after 2. Nf3 Nc6, it is a good move.  
  > **username_4**: After a while you can learn when a piece is really at risk of getting trapped. In double king pawn openings you can often play c3 or d3, useful moves supporting the center, and the light squared bishop is safe, while Black's queenside moves may just open up holes in his position. They aren't as serious as if he moved pawns on the kingside in front of a castled king, but they add up.  Still, getting a bishop nearly trapped can look tricky and worrisome.  
  
  ---
  
  ## 3 answers
  
  ### Answer by username_5 on 2016-09-22. Score: 5
  
  Here are a couple of relevant questions and answers that might help to explain why the bishop move happens:
  
  * [Morphy Defence in Ruy Lopez](https://chess.stackexchange.com/questions/4733/morphy-defence-in-ruy-lopez/4734#4734)
  * [Why is the Ruy Lopez such a common opening?](https://chess.stackexchange.com/questions/226/why-is-the-ruy-lopez-such-a-common-opening)
  
  In summary the main points seem to be that:
  
  * Black loses as much time chasing the bishop as White does retreating it
  * White can gain a long-term advantage from Black's weaker Queen side pawn structure
  
  As you might expect in such a popular opening though it's very finely balanced for both sides.
  
  If as you say you are *not* seeing a6 and b5 in the games you're looking at, you might be looking at games where Black plays the Berlin Defence: 3... Nf6. This is quite popular at the moment in very high level games.
  
  If you want to see some games where the pawn move a6 is played, "putting the question to the bishop", here's a link: <http://www.chessgames.com/perl/chessopening?eco=C70>
  
  
  ---
  
  ### Answer by username_6 on 2016-09-30. Score: 5
  
  The moves Bg5 and Bb5 usually have one the following six purposes:
  
  1. To pin a knight on f6/c6
  2. To *provoke* ...h6 or ...a6, weakening the pawns
  3. To trade White's bishop for its counterpart (usually because the position later will make Black's bishop a better piece than White's)
  4. To take the knight in order to break up the pawns behind it
  5. To take the knight because it defends a central square White wants to occupy with a piece, usually his own knight
  6. To set up the removal of the knight and prepare a mate at h7 once the knight defender is eliminated
  
  If Black responds with ...h6 (say), White can maintain the pin with Bh4. On the kingside, Black is left with a difficult choice: kick the bishop away with ...g5, weakening the kingside, or leave it there as a loose piece.
  
  White often intends to transfer the bishop to the diagonal h2-b8 anyway, when Black's punting the bishop only wastes a tempo and weakens his kingside.
  
  The same is true about the possible destinations of the bishop on the queenside. On the a2-g8 diagonal, it hits the f7 square, which is usually uncomfortable for Black in the KP openings (and obviously good for White).
  
  In some openings, White wants to exchange the bishop, with or without the knight already on f6/c6. In the Sicilian Defense, Rossolimo Attack, White plays 3.Bg5 in reply to 2...Nc6, but Black hasn't moved the d-pawn, so there's no pin. Black doesn't normally play ...a6, because he's not feeling any pain from the Bishop (yet).
  
  In the Canal-Sokolsky Nimzovitch Variation of the Sicilian (also known as the Moscow, although there is a completely different *Prins Moscow* Variation), the line runs like this:
  
  ```
  [FEN ""]
  [Event "B51"]
  [White "Sicilian Defence"]
  [Black "Canal-Sokolsky Nimzovich"]
  [Result "*"]
  [ECO "B51"]
  
  1. e4 c5 2. Nf3 d6 3. Bb5+ {What?? No knight to pin?} Bd7 4. Bxd7+ Qxd7 5. O-O (5. c4) *
  
  ```
  
  ...there's no knight there; White just wants to get rid of Black's good bishop, and saddle Black with a bad one unless he either fianchettoes it on the kingside, or moves all of those pawns (ain't gonna happen). So he invites it to interpose, and trades it off.
  
  In the French Defense, the Alekhine-Chatard attack (strictly speaking, the *Albin*-Alekhine-Chatard), White leaves the bishop on g5 and props it up with his own h-pawn, daring Black to take it. If Black does, he ends up staring down the barrel of White's king's rook on an open file:
  
  ```
  [FEN ""]
  [Event "C13"]
  [White "French Defence"]
  [Black "Albin-Alekhine-Chatard Attack"]
  [ECO "C13"]
  
  1. e4 e6 2. d4 d5 3. Nc3 Nf6 4. Bg5 Be7 5. e5 Nfd7 6. h4 *
  
  ```
  
  Black doesn't play ...h6 here, since there's no point; White will just take on the bishop e7.
  
  In the Ruy Lopez, in 75% of games Black plays 3...a6 immediately. He has no concerns about weakening his queenside; in fact, the pawn storm it initiates often constitutes his main counterplay.
  
  So, these are some illustrations of what the bishop is doing there, and when it may not make sense to chase it.
  
  *Note: Many of these ideas are also present in variations with colors reversed, i.e. ...Bg4 and ...Bb4. The latter is the primary theme of the Nimzo-Indian and Bogo-Indian Defenses.*
  
  
  ---
  
  ### Answer by username_7 on 2016-09-23. Score: -2
  
  "Spanish Bishop" can become very useful and strong piece, especially when it arrives on the c2 square sometimes.
  
  > **Comments:**
  > **username_8**: This answer is too vague in my opinion. Could be more concrete?  
  
  ---
  
  