"Pawns are the soul of chess."
In my head I tend to add something like "yadayadayada. . ." to it. The body of positional knowledge has always been an incoherent set of rules to me. I know about open lines, the center, piece activity, outposts, weak pawns, strong squares, mobility, king safety et cetera. But I never have been able to apply that knowledge properly. I just fiddled around with the pieces, until, out of the blue, some tactical shot appeared. Good or bad. That way of playing made no sense to me, even to that extend that I abandoned playing chess for five years. I solely have been working on a proper study method for tactics, those years.
Together we unearthed the PoPLoAFun system. Nowadays I train daily with the system.
For the first time there is room for something else. So I decided to think about positional play.
For tactical shots, you need lines of attack. That's the LoA of PoPLoAFun. This means that positional play revolves around creating lines of attack. If you think further about this, then you will find that only pawns can create lines of attack.
All of a sudden the body of positional knowledge becomes coherent. In stead of fiddling around with my pieces, I can try to create lines of attack! And for that, I must begin to plan my pawn moves. (So the pawns are the soul after all!)
While reading everything about pawns I can lay my hands on, I was confronted with the importance of the center. I don't have a good grasp of that concept. While reading about the open center, I stumbled upon this position:
 |
| White to move |
The center is not quite open, but after the pawn trade it soon will be.
1.Rxe6 is administered here, and GM Stokfish agrees with +0.67 pawnpoints.
But why is Rxe6 so good?
I can see that the white squares around blacks king become a weak color complex, with the defending bishop removed. I can see that e6 is weak and e5 is a strong outpost. But why is that worth an exchange sacrifice plus +0.67?
It is very strange. The same position with the black rook on e8 or with the white rook on f1 is considered equal, according to gm Stockfish. Where does the urge to sac the rook in the position of this post stem from?
ReplyDeleteI'm clearly missing something, but what?
I had promised myself that I would take a chess break for today, given a lot of activity over the weekend, but this is too interesting. The position is from the below game, move 17, in case people want to look at the original.
ReplyDeletePositional exchange sacrifices are a master-level art, but I would offer the following narrative in support of its positive aspects for White:
- White gains the two bishops in an open position (no center pawn blockages)
- Weak Black e-pawn is created on an open file and on the same diagonal as his king
- Black's light-square complex around the king is significantly weakened (g6 square in particular), which means that White's light-square bishop and the knight on f3 (which now has the Ne5-g6 possibility) are now stronger pieces.
- All of White's pieces (except for the Ra1) are playing well together in the center and kingside, with the queen on e2 also improving itself on move 18.
- White takes over the initiative, as Black now has to work full-time to cover his weaknesses across the board. White basically has all of the fun. From a practical standpoint, that makes the White side easier to play, as well.
The positive evaluation of the exchange sac is due to the improved dynamic piece values for White, along with Black's new structural weaknesses. (Komodo shows a very similar engine evaluation to Stockfish.) This is an area where I think intuition and feel for a situation and the long-term compensation involved are more important than pure calculation. That said, it's very interesting to see how modern engines are no longer materialistic and can effectively work positional compensation into the evaluation function.
[Event "Moscow op 03rd"]
[Site "Moscow"]
[Date "2007.01.29"]
[Round "3"]
[White "Amonatov, Farrukh"]
[Black "Rakhmanov, Alexander"]
[Result "1-0"]
[ECO "C42"]
[WhiteElo "2559"]
[BlackElo "2473"]
[PlyCount "155"]
[EventDate "2007.01.27"]
[EventType "swiss"]
[EventRounds "9"]
[EventCountry "RUS"]
[SourceTitle "CBM 116 Extra"]
[Source "ChessBase"]
[SourceDate "2007.03.07"]
[SourceVersion "1"]
[SourceVersionDate "2007.03.07"]
[SourceQuality "1"]
1. e4 e5 2. Nf3 Nf6 3. Nxe5 d6 4. Nf3 Nxe4 5. d4 d5 6. Bd3 Nc6 7. O-O Be7 8. c4
Nf6 9. Nc3 O-O 10. h3 Nb4 11. Be2 dxc4 12. Bxc4 c6 13. Bg5 Nbd5 14. Re1 Be6 15.
Bd3 h6 16. Bd2 c5 17. Rxe6 fxe6 18. Qe2 Qc8 19. dxc5 Nxc3 20. Bxc3 Nd5 21. Qe4
Nf6 22. Qe2 Nd5 23. Bd4 Nf4 24. Qe5 Rf7 25. Bc4 Qc6 26. Re1 Bd8 27. Qd6 Qxd6
28. cxd6 Kh7 29. Ne5 Rf8 30. g3 Nd5 31. Nd7 Rf7 32. Nc5 Nb6 33. Bxe6 Rf8 34.
Nxb7 Bf6 35. Bxf6 Rxf6 36. d7 Nxd7 37. Bxd7 Rb8 38. Nc5 Rxb2 39. Ne4 Rf8 40.
Be6 a5 41. Bb3 a4 42. Bxa4 Rxa2 43. Bb5 Ra3 44. Bf1 Kh8 45. h4 Re8 46. Bg2 Ra7
47. Rd1 Rae7 48. Rd4 Ra7 49. Bf3 Ra3 50. Kg2 Rf8 51. Be2 Ra2 52. Bd1 Rb2 53. g4
Kh7 54. Kg3 Ra2 55. g5 hxg5 56. hxg5 Rfa8 57. Bg4 R2a3+ 58. f3 Rf8 59. Rd5 Kg6
60. Rd6+ Kh7 61. Bh5 Ra1 62. Bg6+ Kg8 63. Rd2 Ra3 64. Bh5 Kh7 65. Rh2 Kg8 66.
Bg4 Re8 67. Bf5 Re5 68. Kg4 Raa5 69. Bh7+ Kf7 70. Rb2 Ra7 71. Rb6 Rc7 72. Bg6+
Ke7 73. Rb8 Kd7 74. Rg8 Kc6 75. Ng3 Re6 76. Be4+ Kc5 77. Nf5 g6 78. Nh4 1-0
I found the position (and game) on Chess Tempo. I entered the position into Fritz 11 (running Stockfish 9 64) and also ran Stockfish 10 on Chess Tempo, both programs running overnight. Initially (before I went to bed at midnight), both programs oscillated between 18. Qe2 and Qe1, with the score over 1.2 with a slight edge for 18. Qe2. The primary response for Black was 18. ... Qc8. This morning, both programs gave 18. ... Qd7 as best; the evaluation had dropped to approximately 0.80.
ReplyDeleteChess Admin gave an admirable description of the reasons why White has a significant advantage, albeit not a forced (tactical) win. I thought of some (not all) of his points. One additional point that is not mentioned explicitly is the difficulties Black faces developing and coordinating his pieces. In particular, if the Black Queen moves to c8 to protect the e6 Pawn then the Black Rook on a8 is essentially useless. 18. ... Qd7 (or 18. ... Qc8) both seem to "defend" the e6 Pawn and also the b7 Pawn, but this means that the Black Queen takes on two functions, which provides a clue for how White should try to exploit that overloading. There doesn't seem to be much (if any) compensation for Black in just letting the e-Pawn disappear without a fight.
The two Bishops in an open position are capable of striking almost as many squares as the Queen, so this is an ideal position for them.
All of these factors are small in and of themselves, but when combined, illustrate Steinitz's notion of "the accumulation of small advantages" and the principle of two weaknesses. Eventually, White WILL have the opportunity for the tactical exploitation of all these factors.
Let's call the position from the post "A". Let's call the same position with blacks rook on e8 in stead of f8 "B".
ReplyDeleteThe exchange sacrifice 1.Rxe6 in position A is rewarded with +0.67. The same sacrifice in position B is rewarded with exactly 0,00 points. According the moves given by Stockfish, accepting eternal check is the best thing white can do after the sac in position B.
What on earth am I missing?
A Black Rook on e8 contests the e-file. It also defends the e6-Pawn ahead of White's anticipated "attack" on it (while also avoiding tying down the Black Queen with that task) and makes luft for the Black Bishop to retreat to f8 (if needed). With the Rook actively defending the e6-Pawn, the Black Queen is freed up for mischief elsewhere (like b6, with the possibility of "protecting" some of the white square complex on the kingside). In a position with structural minuses, it is very important to find dynamic counterattacking possibilities. So goes the "theory."
DeleteI wouldn't have thought that the difference in Rook position was worth 0.67, but there it is. Grandmaster Stockfish has the final word because of its ability to “see” the kinds of balancing operations in the far future that we mere mortals cannot “see.”
I suspect that whether the e6 pawn can be conquered or not is the most important cause of the difference in assessment.
DeleteYou sac the exchange ( -1,75 ) but you win the bishoppair ( 0,5 ) and sooner or later the pawn e6 (1.0) =-0.25. You win the center and you get a strong attack to the black king
ReplyDelete( i was watching gm stockfish playing the position )
I can understand Tempo's troubles in assessing the position.
ReplyDeleteFirst of all: the bishop pair is not 0.5 worth. It really depends on the influence of the bishops.
The black knights in position "A" seem pretty well placed, and in general: if your knights are reasonably close to your king (which they are here) - you have a hard time to get anything out of your attack.
That the pair of bishop is not the reason of 0.5 compensation can be shown by the difference between position with rook on f8 and position e8.
Clearly, we all can understand the pawn on e6 is weak. I guess the e6 pawn is hard to defend, so might get lost.
After Qe2 (next move) --> If the black queen defends on d7 then she can be attacked with Nf3-e5. And if she moves on d6 then there is Nc3-b5 of dxc5 - though I dont know if that yields anything.
To be honest, I am with Tempo: I can not evaluate the rook-sac properly.
I would not sac the exchange in this position. At best I do understand some compensation, but would not have evaluated it so high.
https://www.chess.com/article/view/the-evaluation-of-material-imbalances-by-im-larry-kaufman
ReplyDeleteThe Evaluation of Material Imbalances (by IM Larry Kaufman)
THE BISHOP PAIR
The bishop pair has an average value of half a pawn (more when the opponent has no minor pieces to exchange for one of the bishops), enough to regard it as part of the material evaluation of the position, and enough to overwhelm most positional considerations. Moreover, this substantial bishop pair value holds up in all situations tested, regardless of what else is on the board. This large a bishop pair value is surprising because in the opening grandmasters will often give up the bishop pair to double the opponent's pawns or to gain a mild lead in development, factors which are generally not worth half a pawn [DH: Since at the very start of the game a tempo is worth roughly a third of a pawn - and more later! - it is worth losing a tempo to save the bishop pair, but if you can gain two tempo by giving up the bishop pair that may be worth it in the short run!]
One explanation was provided by GM Timoschenko; in the opening, with all the pawns on the board, the knights are worth more than the bishops (excluding any bishop pair bonus), so the player who trades bishop for knight in the opening is already getting some compensation for his lost bishop pair. Also, the bishop pair is worth less than half a pawn when most or all the pawns are on the board, and more than half a pawn when half or more of the pawns are gone.
Once a few pawns are traded off, though, the bishop pair is really worth every bit of the half pawn average, if not more, as illustrated by the fact that in several openings (Marshall [DH: Marshall Counterattack in the Ruy Lopez], Petroff) Black obtains excellent drawing chances by giving up a pawn almost solely to obtain the bishop pair. I was particularly struck by a remark in Chess Life by Garry Kasparov who, while annotating a title game with Nigel Short, implied that he had a probably won game once he won the bishop pair in a closed Ruy [DH: Ruy Lopez], even though there were no open lines, no other advantages, and it took him some tempi (Nf3-h4-g6xf8) to take the bishop.
One rule which I often teach to students is that if you have the bishop pair, and your opponent's single bishop is a bad bishop (hemmed in by his own pawns), you already have full compensation for a pawn. In other words, if most of your opponent's pawns are fixed on one colo and you both still have both bishops, it is worth losing a pawn to trade a knight for his "good" bishop. I have often won games by doing so. Kasparov has said something similar, at least with respect to the King's Indian Opening [DH: likely where Black plays a knight to d4 or f4 and black wins a pawn with BxN PxB QxP opening the black king's bishop].
Why is the bishop pair so valuable? One explanation is that the bishop is really a more valuable piece than the knight due to its greater average mobility, but unless you have both bishops the opponent can play so as to take advantage of the fact that the bishop can only attack squares of one color. In my opinion, another reason is that any other pair of pieces suffers from redundancy. Two knights, two rooks, bishop and knight, or major plus minor piece are all capable of guarding the same squares, and therefore there is apt to be some duplication of function.
With two bishops traveling on opposite colored squares there is no possibility of any duplication of function. So, in theory, rather than giving a bonus to two bishops, we should penalize every other combination of pieces, but it is obviously much easier to reward the bishop pair. It is partly for similar reasons we say to trade pieces when you are ahead; if you have two knights against one (with other pieces balanced), the exchange of knights means that you are trading a partially redundant knight for one that is not redundant.
...
Largely by chance, I recently ran across the following, from Euwe and Kramer's "Middlegame: Book One - Chapter 4: The Exchange"
ReplyDelete"More interesting than material equivalents, however, is the question of positional compensation...in cases of compensation without a pawn, the side weaker in material needs two kinds of advantage in the position. The possession of two Bishops is always a dominating factor. Two Bishops plus a protected passed pawn or two Bishops plus a weakened enemy King position must be reckoned as full compensation."
My impression is, that if the advantage of bishops is demonstrated in an example, then in this very example the bishop pair is really superior.
ReplyDeleteHowever, I am very sensitive to statistics: I looked at various positions and tried to find out why one opening is superior to an other opening. My result: it really depends on the position, the pair of bishops included.
I am not saying the pair of bishop is never an advantage. It can be. And maybe in 70% of the positions it is. And I guess part of my opening success is exactly based on the strange positions where the pair of bishop is no advantage. See: my Rat-Defense (1.d4 d6) often leads to an endgame, where white has the pair of bishops, but black has already his king on the queenswing. Here the black advantage of having one more piece on the queens wing (the king) is much more valuable than the pair of bishops for white.
Here an opening, where black's last move is going after the pair of bishops. You can not say that this is a totally blocked position, so the pair of bishops should count for something.
Nevertheless, after playing 10...Ng4 black can not really enjoy his pair of bishops.
The statistics are telling us: 57% wins for white versus 13% wins for black after 10...Ng4.
Statistics tell the truth. The advantage of the pair of bishops is non-existant, whereas the advantage of getting rid of the bad light squared bishop is probably the reason why the statistics are so poor for black here.
1. Nf3 c5 2. c4 Nc6 3. d4 cxd4 4. Nxd4 Nf6 5. Nc3 g6 6. e4 d6 7. Be2 Bg7 8. Be3 O-O 9. O-O Bd7 10. Qd2 Ng4
I guess the key evaluation to see here is: white has a bad bishop on e2 after he plays f2-f3 at some point.
It is better to get rid of this bad bishop, which means: white shall seek to hand the pair of bishops to black.
But is a bad bishop a disadvantage of -0.5?
No, not really. Especially here, where the position isnt blocked. There is still the chance of pawn moves later in the game, and the Be2 could become better.
Thinking about all this gives me the idea of looking at random positions from real games and try to find out why the evaluation is like it is. Not sure if stockfish is the best engine for that purpose, though.
@ Munich:
ReplyDelete"Not sure if stockfish is the best engine for that purpose, though."
I don't remember who suggested it (perhaps it was you, or Aox), but the online Stockfish Evaluation Guide is a goldmine for deciphering computer evaluations.
Link: Stockfish Evaluation Guide
When I first started using it, I just tried to see which component(s) of the evaluation were significant. After some use lately, I "discovered" the tabs on the upper left labeled "Evaluation term - Global functions - Table - Graph". This can be combined with the right side "Read - Edit - Save" and the FEN/PGN entry text box. You can drop FEN or PGN into the box and it will track (and evaluate) every position that you move to. The left/right arrows work to move forward and backward through whatever move sequence you enter, after you've entered it. You can drag and drop pieces/pawns and the diagram will automatically update, giving the main evaluation. On the left side (after selecting the Table tab), you can see the major factors used in that evaluation. This feature, used in conjunction with Chess Tempo's Database, is really helpful for understanding what exactly is going on in the evaluation!