KID fiancetto variation - reason for c6 after Nd7

I've noticed that when black goes Nd7 in the KID fiancetto variation, then often he follows up with c6. What is the main reason(s) for this? Especially, I'm asking this question as often the d6 pawn afterwards becomes subject for attack by white. First I thought the reason was mainly defensive to hold white knights away from b5 and maybe even d5, but I don't really see this being such a threat. Then I figured the reason for c6 was do go d5 at some point, but rarely does black indeed play this move, so I'm unsure as to why black usually does go c6 and thus creates this target on d6.

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1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.Nf3 O-O 5.g3 d6 6.Bg2 Nbd7 7.O-O e5 8.e4 c6 ( 8...Re8 9.h3 c6)

• Can you add a diagram with an exact position? Or the moves to get to one? Commented Apr 1, 2017 at 19:32
• Yes, sorry! Not sure how to add a diagram, but this would be the move order. 1.d4 Nf6 2.c4 g6 3.Nc3 Bg7 4.Nf3 O-O 5.g3 d6 6.Bg2 Nbd7 7.O-O e5 8.e4 c6.
– acye
Commented Apr 1, 2017 at 20:26
• Another point is to enable to queen to go to squares like a5, don't have time for an answer ATM. Commented Apr 2, 2017 at 9:00

First of all, to sit back and wait isn't a good strategy for black, as white has many useful moves to make: h3, Be3, Qc2, Rfe1, Rad1. If white can get these moves in with black doing nothing, white will be clearly better.

So black has to look for counterplay. Most of black's options involve c6 to activate the queen on the d8-a5 diagonal. If you absolutely don't want to move the c-pawn, then one of the few options left is to play exd4 followed by Nc5 and a5. This is playable, but not popular, as white can place an annoying knight on b5, see Giorgiev vs Ilincic, Belgrade 2000.

Black can also try to play exd4 and Nc5 without a5 (instead Bd7, a6, and so on). The game then can get sharp, but current theory says white is comfortable.

In summary: Black plays c6 to get needed counterplay. The other options to get counterplay aren't quite as attractive.

• Thanks for that! I guess I didn't really see the Nb5 maneuver from White's side as particularly threatening.. I will look into the plan you you mentioned of black playing c6 to open the d8-a5 diagonal; that makes sense.
– acye
Commented Apr 3, 2017 at 6:00

I'm unsure as to why black usually does go c6 and thus creates this target on d6.

The key point is this: it's not a weak point unless it can be attacked, and white can currently only attack it with one bishop, which is easily defended against. If white tries to attack it further, they can only do so by opening the d-file, which ends up removing the weakness (9. dxe5 dxe5, for example) and also demonstrates the usefulness of 8...c6 (it is covering d5).

As for why black is playing c6 over other options: the position in the centre is in considerable flux, and black doesn't know where they want the rest of their pieces until the centre settles (e.g. if white closes with 9.d5, the rook doesn't want to be on e8 and instead was perfectly fine on f8). 8...c6 is a move that retains black's flexibility and gives white another chance to act decisively. As previously mentioned, it is very useful if the centre opens with 9.dxe5, but it is also useful if white advances 9.d5, because after 9...c5 white can't take en passant and black gets a structure similar to the Czech-Benoni but with more comfortable development.

Of course, white is free to maintain the tension, continuing the theme of the fianchetto response to the KID.

Edit: in the exd5 exd5 lines, you are possibly wondering about the vulnerablity of d6, with the pawn defending it having advanced to c6. This is an important thing to think about, and I can't answer it from my own experience, but in practice the g7 bishop retreating to f8 is enough to cover it (swapping off the the bad bishop in the process :-) )

• Thanks! Actually I've seen in my reseach that it's often black that takes on d4 and thus open up for pressure on d6. This in particular seems odd to me as it seems to simply create a nice strategy for white... I'm studying this opening to use as white, but I feel if I'd be black I'd be making non-comittal waiting moves and, not c6 and and not exd4, but waiting for white to show his colors.
– acye
Commented Apr 1, 2017 at 22:51
• I'll admit I don't know the specific theory here: I only suggested what I thought was the most principled response. I think that there aren't many non-committal moves at the point you've given (The Nd7 doesn't want to go anywhere, and neither does Rf8) and I wouldn't be surprised if the research you've found allows for dxe4 after a similarly compromising move from white, since they also have the same problems. I can't give you the exact details, though. Commented Apr 1, 2017 at 23:06

The purpose of c6 move is below .

• c6 stops the Knight on c3 coming onto d5.
• It makes a square for the Queen to come on c7 or sometimes gauge an eye over the Q-side . Q comes to a5 and then attacks b4.
• It eventually sometimes supports b5 which makes a Q-side pawn push.
• Thanks! Regarding point #2, could you perhaps point me to a successful implementation of Nc3-d5 in a case where black did not go c6?
– acye
Commented Apr 3, 2017 at 22:41
• You can go in chessgames and find out the Games which have Nc3 to d5 . You have an option from Opening explorer and see any games in that particular variation . Commented Apr 4, 2017 at 13:00