Nimzo Indian : when to trade on c3

Hi,

I just started studying the Nimzo Indian (and chess in general :). The exchange of black's DSB against the knight is a recurring theme in many lines of this opening. As far as I understand, this either delays development (if the Queen recaptures) or inflicts double pawns on the c-file for white. More importantly, it helps keeping control of the e4 square, by removing one of its defenders.

But... just when I thought I got everything figured out, I stumbled upon several Nimzo Indian games where the bishop instead of capturing simply retreats at some point.

Are there rules that explain why/when/how to trade the DSB against the knight in this particular setup?

To be specific : here is a sequence of moves used by Carlsen against Nakamura.
1.d4 Nf6 2.c4 e6 3.Nc3 Bb4 4.f3 d5 5.a3 Be7

Any reflexion on this fascinating question will be much appreciated.

Ecureuil

Yes, Nimzovich himself used to capture ...Bxc3 and he used to follow up with ...d6 and ...e5. Later it was found that black sometimes does better retreating his bishop to e7 or a5, keeping the bishop's pair. In the game that you cite black keeps his bishop's pair and gives a tempo: Bf8-b4-e7, but the move a3 gained by white does not matter. The move 4 f3 has weakened the black squares e3, f2, g3 in white's camp thus it makes sense to preserve the bishop for later. In some sense you can see 4...d5 and 5...Be7 as trying to refute 4 f3, weakening the black squares and occupying the natural square for Ng1. The move 4...d5 controls square e4, so the bishop can be relieved of that task.
The general rule is that black should only capture ...Bxc3 if he can fix the centre. With a fluid centre the white bishop's pair is worth more than the weakening of the doubled pawns.

In that specific line, I play Bxc3 (and it's the main line)

Don’t like rules of thumb but here‘s one practical approach: when prompted with a3 take the knight.

(I know the exceptions but that‘s a bit difficult to explain)

Here is a famous example of black taking ...Bxc3 without being prompted by a3.

Here is a game, which @tpr doesnt know, where black takes on c3 without being prompted by a3. White mates in eight moves:



And here is a game where black waits with taking on c3 until white played a3. This time black mates in seven:



Lesson: wait until white played a3.

@nh78 April 1 was 12 days ago.
I give 2 counterexamples from high level games.
Carlsen gets prompted and does not take.
Fischer did not get prompted and took.
So the prompt = take, no prompt = no take rule seems not valid.
My rule: if you can fixate the centre pawns with your pawns on black squares, then take, prompted or not.
If you cannot fixate the centre pawns with your pawns on black squares e.g. when you have played ...d5, then retreat when prompted if you can.

Ok thanks a lot @tpr, @nh78 and @Sarg0n for your interesting views on the matter. Of course rules of thumbs are not perfect, but it's a good starting point for a beginner like myself.

Nimzo-indianly yours,
Ecureuil

Don't think that after a3 ...Bxc3 is a blunder and you gonna lose therefore.

Here an otb tournament game of mine which I lost where you usually don't take on c3 after a3. White was GM Sanikidze, FIDE-Elo > 2600.

evfcrerrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr