What are the reasons why I should not try to take a Knight with my Bishop if it'll result in doubled pawns?

Question

For instance, in the Ruy Lopez, after

[FEN ""]
1. e4   e5
2. Nf3  Nc6
3. Bb5  a6

why shouldn't I take the Knight?

4 Bxc6 dxc6

Now Black has a doubled pawn.

It isn't a very popular line of play, which is why I think I shouldn't play it; but as to the principle, is it because I'm opening up Black's game? I don't see any significant advantages/disadvantages for either side.

Answer 1

This is a variation that was played fairly frequently, but it has been more or less worked out to a draw, so it is less common at the top levels now.

The Ruy Lopez is a very concrete opening, and the capture on c6 has to be carefully considered as it relates to the exact position.

In terms of opening principles, you're giving up a bishop for a knight in an open position. If you could take the pawn on e5, it might be good, but the pawn is protected via the tactical shot 5.Nxe5? Qd4! when white has basically given up the two bishops for very little compensation in a wide open position.

Another downside to Bxc6 is that the black's light square bishop is developed by dxc6, allowing it to come to g4 without waste of time. Indeed, one of the most critical lines continues 5. O-O Bg4 6. h3 h5 when black is offering a piece for attacking chances along the h file.

With all of that said, this is a very common motif in the Ruy Lopez (Bxc6). The pawn structure after d4 and exd4 is very good for white. If all of the pieces were traded off, white would win the king and pawn endgame by making a passed pawn on the kingside and black cannot make a passed pawn on the queenside.

There are also many cases when spoiling your opponent's pawn structure is very good. For example, if black has castled kingside, and a bishop can take on f6 and force ...gxf6, this is almost always good for white. The king becomes very exposed with the g file open. In the Spanish Four Knights, one player or the other will very frequently take on c6 or c3.

Answer 2

If the doubled pawns created after taking the Knight leave a b- or g-file half open against your castled King, it might be relatively easy to create an attack against your King if the opponent's Rook leverages the half open b- or g-file by building pressure against your King's castle.

Answer 3

There are a few disadvantages:

1. You trade your light-squared bishop, your best attacking piece.
2. You give Black the bishop pair.
3. The likely followup is an exchange of queens and an early endgame.

If you like to attack and don't like to play against bishop pairs, don't play this variation.

Do play this variation if you are confident in your play with two good knights, fear having queens on the board, or like to play endgames. The doubled pawns are a clear endgame advantage, if you know how to "shorten" the middle game.

Answer 4

• Some impressive people consider bishops marginally stronger than knights, though the board position is critical. Reference below.
• The black Q is freed, perhaps saving black a tempo.
• The black w-squared B is freed, saving a tempo.
• The white w-squared B is gone, after 2 moves were spent on it.
• Black's pawns are doubled, but they still hit the d-file. Not so bad.

In the next 5 moves, it is possible for black to develop all 3 remaining minor pieces, the queen, and castle. In short, black has a flexible position.

Edit

Some people have issues with the statement about bishops being stronger than knights. So check this Wiki page (OMG Wiki). You'll see a chart down under 'Alternate Valuations.' You'll see references that include names of knowledgeable people that rate the bishop higher. No one listed on the chart rates knight higher, though many rate them equal.

Answer 5

Let's see, what is the original question? The poster thinks that taking a knight with a bishop should be good if it results in the opponent getting doubled pawns. And the poster also specifically asks about bishop takes knight. I will address both parts of the question.

Of course, everything depends on the position. So it is difficult to give a general answer. However, I shall try. But keep in mind that chess does not have a general solution, only heuristics to go by. And sometimes they fail.

Doubled pawns

Presumably because we "know" that doubled pawns are bad. However, this does not have to be the case. As the poster already found out, because in the given example sometimes people play Bxc6, but they also play Ba4.

It is all about control.

Pawns are the strongest when they are next to each other, in line. Like in the starting position. Why? They control all squares one row in front of them. Every pawn you move also creates some weakness. If I move my pawn from b2 to b3, the a3-square is weakened, because no pawn can defend it.

Disadvantages of doubled pawns:

• the pawn that captured now controls different squares than before
• if the doubled pawns are isolated, they are really weak. The opponent can put a piece in front of the doubled pawns that can never be chased away by a pawn (same holds when the neighbouring pawn is already ahead: if Black plays b7-b5 in the example structure, the square c5 is very weak
• they are in each other's way, so they move slower

Advantages of doubled pawns:

• They control a lot of consequent squares. In the example they control b6, b5, d6 and d5.
• A doubled pawn means a (semi-)open file. Which can be good for your rook.
• A doubled pawn means a diagonal has been opened (like in the example: the c8-bishop now can be developed)

All in all, doubled pawns are good for defending, but not for attacking.

Bishop takes knight

The value of a bishop or knight depends on the position, of course. Roughly it can be said they are about equal strength. But they have different advantages.

A knight can jump over pieces, so it is a great blockading piece. And it is strong in closed positions. Also, it can reach any square of the board. However, a knight is a slow-moving piece. For instance, it takes several (six) moves to go from a1 to h8.

A bishop can make long moves. For instance, it takes only one move to go from a1 to h8. This means it works best in open (many diagonals) positions. However, it can only reach half of the squares. And if the bishop is blocked by a pawn chain, it can be passive and bad.

However, the pair of bishops is considered to be a real asset. You have the advantages of the bishop, but not the disadvantage of only controlling half of the squares. Also, it is up to you to decide when to give up the bishop pair and convert to some other advantage.

Back to the example

To come back to the example: the move Bxc6 hands the bishop pair to Black. Since this is very early in the game, Black can handle accordingly and play with the two bishops (and try to open up the game). And the doubled pawns are not that weak.

Another example of doubled pawns, where the bishop does take the knight is in the Nimzo-Indian defence. After

[fen ""]

1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.a3 Bxc3+ 5.bxc3 

These doubled pawns are a little bit different than the ones from the Ruy Lopez example. The most important detail: the c4-square is weak. No pawn can control it. A strategy for Black is to play against this pawn by playing d6, e5, c5, b6, Nc6-a5 end Ba6. But that is something for another time...

Answer 6

This is more or less equal, so not good for white, who is striving for an advantage. The c pawns are doubled, however, black has the bishop pair. A doubled pawn is worth somewhere 25cps(centipawns, 1 hundredth of a pawn), while the bishop pair 50cps on average, double that, so the trade on c6 was not good at all, the white advantage evaporated. Black is fully ok in above position, unless his opponent is Fischer, who has won many great games with the Exchange. If white does not trade queens with d4, the best black plan is to play Qd6 and castle long, then start a king side pawn storm with f7-f6, g7-g5, etc.

Answer 7

The knight pin by Bg4 is annoying. Playing h3 costs a tempo in an open game.