Why is it better to take with the knight than with the pawn in this position?

Question

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I recently had a chess game in which I played as white and the position was as shown in the picture. I chose the move cxb3, but the chess engine states that the move Nxb3 is better. Why is it better to take with the knight rather than the pawn in this position?

Answer 1

Why is it better to take with the knight rather than the pawn in this position?

Taking with the pawn is bad for the pawn, the knight and the bishop while taking with the knight is good for all those three pieces.

First, the knight

With the pawn on b3 the knight has no future. It is tied down in a passive position on d2 having to defend the weak pawn on the open file. Furthermore it is blocked from moving forward to either e4 or c4 by the black pawn on d5 which is now a supported passed pawn. So, the pawn capture has even improved the black pawn on d5.

With the knight on b3 the knight is much better. For the moment it is protected by the pawn on c2 but it could also move to d4, a fine outpost from which it blockades the black pawn on d5 (which is no longer passed) and from which it can't easily be moved. As a bonus it also protects the pawn on c2 freeing up the bishop if it wants to move.

Alternatively, possibly after connecting the rooks by castling or moving Kd2 or Ke2, the knight could move to c5 threatening to either exchange itself for the bishop or blockade the a7 pawn on a6.

Another possible route for the knight would be Nb3-a5-b7-d6. Although black would have to play badly to allow this.

The knight has a much, much brighter future on b3.

The pawn

On b3 the pawn is much weaker than on c2 where it anchors the bishop and prevents the black d5 pawn from being passed.

The bishop

With the pawn on c2 the bishop has a role protecting the pawn. If the pawn moves to b3 then the bishop has to move to the passive square c2 to protect the pawn.

At the end of the day black is still a pawn up but that pawn is weak, black's bishop is bad and white is ahead in development.

Answer 2

Disadvantages of cxb3:

1. Black's d pawn becomes a protected passed pawn. This becomes increasingly relevant as fewer and fewer pieces are left to stop it from promoting d4-d3-d2-d1=Q.
2. The c pawn loses a natural defender (bishop), and must now be defended by a poor defender (knight). Bishops defend pawns better than knights because they are harder to distract/kick away, and can do other things while defending. But wait, can't we defend our new b3 pawn with Bc2? We could. But then our active attacking+defending bishop becomes a passive defender!
3. The bishop loses a defender. Maybe it's not relevant now. But it might play a role in the future. LPDO.

Advantages of Nxb3:

1. The knight is promoted from the 2nd rank to the 3rd!
2. The knight is one step closer to centralization. (Although, admittedly, there is an alternative path to knight centralization: Nf3-Nd4.)
3. The knight gains a safe outpost. (An outpost is a square defended by a pawn.)
4. The knight controls more squares (a5, c5, d4).

Answer 3

Just look at the activity of the knight. Because of the black pawn on d5, the c4 and e4 squares are out, f3 leads nowhere and even rerouting to e3 through f1 for example does nothing.

Now look at the activity of the knight on b3. It can jump to c5 and start making threats, it can jump to a5 and blockade the a-pawn with a bunch of interesting jumps from there, it has a nice potential square on d4 that controls a lot of the light-squares of the opponents bishop and let's it jump to b5 making threats on c7 and d6. Activity, activity, activity.