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  1. Forum
  2. Game analysis
  3. Why is Bg7 ...

... a stronger move than Bxc3?

1r2r1k1/5p2/b1pq1bp1/p2p4/6P1/PPN2Q1P/K1P1NP2/3RR3 b - - 2 25

Here are some intuitive reasons I can give for why you might want to preserve your bishop by moving to g7 instead of taking on c3. First, however, note that the result of the sequence 1. .. Bxc3 2. Nxc3 (not 2. Qxc3 Rxe2) is that you've effectively traded your dark-squared bishop for white's knight on e2. This fact will help us understand the consequences. First, why do we want to keep the bishop on the board?

• Black's dark-squared bishop ties in really well with his pawn structure. Nearly all black pawns are on light squares, so the bishop is not bothered by them at all, making it a better piece.
• Because the bishop ties in so well with the black pawns on g6 and f7, he is also an excellent defender of the kingside. If black takes on c3, he will immediately face problems with his king, because f6 will be weak. White could put a pawn on g5 and try to get his knight to f6, where it would be very close to the enemy king and nearly invulnerable.
• The bishop is also looking towards the side of the board where the white king is located, which could help black become dangerous soon.

What about white's knight on e2? Is it worth trading him off? Not really.

• Black has pressure on e2 as well as on c3. After 1. .. Bxc3 2. Nxc3, both pressure points are gone: nobody is attacking c3 anymore and there is no longer a white piece on e2.
• The knight is also blocking white's rook on e1 from participating.

Finally, a more abstract reason and principle:
• Black has the bishop pair, which is generally a good thing because two bishops can work together quite well. Taking on c3 would give up this advantage.

In short, black's bishop is a very good defending and attacking piece, and it's not worth it to trade him for the knight on e2. Hope this helped.

Agree with #2.
A bishop is worth more than a knight. You should never trade a bishop for a knight without good reason to do so.
You are a pawn down. If you are a pawn down, then you should trade pawns, not pieces.
You bishop's pair compensates the pawn down.

@tpr said:
> A bishop is worth more than a knight.

The way you said this it is at best a half-truth. Paraphrasing John Nunn (Understanding Middle Games) bishop and knight are worth the same in "net material". Depending on the specifics of the position, sometimes the bishop is worth more and sometimes the knight is worth more. As it happens positions favouring the bishop occur more often than positions favouring the knight. Therefore "in general" the bishop is considered a bit more valuable than the knight.

Still, if that is the case in a specific position needs to be analysed. Generalisations don't help in doing this. i.e. in queens indian and dutch variants black may exchange the bishop b4 for the knight c3 not only to double whites c-pawns but also weaken whites control of the light squares in the center as the knight c3 controls e4 and d5. Black will fianchetto the bishop c8 to reinforce this control , along with the pawns on e6 and f5 and the knight on f6.

krasnaya

Many thanks to @MessyAnswer & @tpr & @krasnaya for this great insight!

My takeaways:
. think twice before trading a bishop with space for a knight
. do not trade the main defender of your kings position
. do not trade a bishop that is pointing to the enemy king
. always maintain pressure
. keep your bishop pair
. beeing a pawn down, one should not trade pieces, but pawns

phaseno2