What is a backward pawn?

[bob]

Last time I checked the definition of "backward pawn", an "isolated pawn" that was not a "passed pawn" is backward too ...

[d]6k1/8/2p5/8/p7/2P5/1P6/6K1 w - - 0 1
You want to say a4 and c6 are backward too?

Yes. Neither can be defended by friendly pawns. backward is just a special case of isolated, or vice versa. Both are weak. I only evaluate "weak" pawns in Crafty, for example. There are various levels of "weak" to be sure (white pawns on c5/e5, black pawns on c4 and d3. That d3 pawn is REALLY weak. Remove either the c5 or e5 pawn and it is not so weak as a piece can help it advance and liquidate. But with both c5/e5 the d3 pawn simply can not move, period.

[Ferdy]

[d]6k1/3p4/1p6/p3p1p1/P3P2p/1P1P3P/6P1/6K1 w - - 0 1
I consider b3, d3 and g2 as backward for white. The engine will strive to remove this bacward pawn by supporting the push by pieces. For example white will play b4, if axb4 and a white piece takes b4 too, what we have now is a black backward pawn in b6, the white a4 pawn is not backward because it is already in the fourth rank. So black will prepare something if ever white will achieve the push, because if black will not take the white's b4 pawn push, white has the posibility now of either moving b4b5 grabbing space or b4xa5.

[d]6k1/3p4/1p6/4p1p1/P3P2p/3P3P/6P1/6K1 w - - 0 1
So why on Earth b6 should be backward and a4 not? Those pawns already get different psqt values for 4th and 3rd rank respectively, but apart from that, what is the difference between them? They both can not advance, it is 1 vs 1, some bonus for pawn control only for a4 is OK, but that would be 5-8cps, we are talking here of giving 20-30cps and more penalty for a real backward pawn. Is it possible that b6 gets penalised so much?

And also why d3 is backward? It can not advance, but black's d pawn also can not advance past the 6th rank, and it is an equal distribution of resources, 2 vs 2, neither side gets anything special from that situation. So that I think, although d3 could be penalised, this is wrong in practical terms.

To ask you one question, Ferdinand, how is Deuterium able to play so strong when it understands backward pawns so poorly?

There is a book "Pawn Power in Chess" by Hans Kmoch that says a backward pawn is a half-free pawn on the 2nd or 3rd rank whose stop square lacks pawn protection but is controled by a sentry. I generally coded in this way. Tuning these values is certainly possible. Still there are a lot to change and tune, the state of the affair is to minimize the bugs

[Ferdy]

Hi all,

Both of you miss this point: The definition of "backward pawn" in a chess engine is an extremly bold definition designed solely to be awarded a single, hefty penalty later

.
So what is not extreme? Why it is bold?

Distinguish carefully:
"Backward pawn" for a chess player <-> "Backward pawn" for a chess engine.

Backward pawn from a human generally works fine when applied to engine.

This is a main problem in this forum: Chess knowledge representation is inadvertly mixed with chess engine logic.

There is no problem in this forum, we are open to discussion.

The successful chess programmer is something of a hacker a this point. He expects something mathematically sound, that works for any random position his engine may encounter. Any exception to the rule could turn into a bug.

The succesful chess player on the other hand is mainly concerned about his intuition. He sees one position and then believes his has seen them all. Small exceptions to the rule are accepted as normal.

So please keep in mind the different mindsets of chess programmers and chess players.

To get a feeling for a working world class chess evaluation consider:
http://www.top-5000.nl/ZW_Rybka_Fruit.pdf

You will see that the evaluation is extremly limited. There are very few surviving concepts.

If you want to improve on that, i think the following principles should be adhered too at least:

A feature must have low volatility. Think about it: All positions with the same feature get the same penalty. If you award innocent backward pawns the same penalty than really backward pawns you asking for trouble. Both of you consider some innocent pawn structures, mixing them up with backward pawns. Big blunder!

Features must be orthogonal to each other. If you work on backward pawns, you must think about your other pawn features too. Overlap should be minimal. If you dont have othogonal features, your parameter estimates will later fight each other, emitting lot of noise. This error can make linear parameter estimation fail!

Concluding:
Interesting work on the semantic of backward pawns, but the logic is currently flawed.

Sorry, i currently dont have time to work on this positively. Maybe later.

Oliver

Thanks for raising some interesting points.

[bob]

[d]6k1/3p4/1p6/p3p1p1/P3P2p/1P1P3P/6P1/6K1 w - - 0 1
I consider b3, d3 and g2 as backward for white. The engine will strive to remove this bacward pawn by supporting the push by pieces. For example white will play b4, if axb4 and a white piece takes b4 too, what we have now is a black backward pawn in b6, the white a4 pawn is not backward because it is already in the fourth rank. So black will prepare something if ever white will achieve the push, because if black will not take the white's b4 pawn push, white has the posibility now of either moving b4b5 grabbing space or b4xa5.

[d]6k1/3p4/1p6/4p1p1/P3P2p/3P3P/6P1/6K1 w - - 0 1
So why on Earth b6 should be backward and a4 not? Those pawns already get different psqt values for 4th and 3rd rank respectively, but apart from that, what is the difference between them? They both can not advance, it is 1 vs 1, some bonus for pawn control only for a4 is OK, but that would be 5-8cps, we are talking here of giving 20-30cps and more penalty for a real backward pawn. Is it possible that b6 gets penalised so much?

And also why d3 is backward? It can not advance, but black's d pawn also can not advance past the 6th rank, and it is an equal distribution of resources, 2 vs 2, neither side gets anything special from that situation. So that I think, although d3 could be penalised, this is wrong in practical terms.

To ask you one question, Ferdinand, how is Deuterium able to play so strong when it understands backward pawns so poorly?

Think like a computer. d6 is a "weakly backward pawn", As is d3. We call that a "wash". So no side has any advantage there. If one side has more of those weak pawns than the other, they then become a real disadvantage.

[carldaman]

My take on this is that you are somewhat mixing terms.

A pawn that is defended by a pawn is not considered backward in any book I have (g6 in your first example as it is defended by h7). The fact that it can not safely advance is not so important when it is perfectly safe where it is. If you want to talk about it being immobile, that is a different issue.

the "unopposed" requirement stems from the rook, in the books I have read over the years. A pawn that is backward (can not be safely defended by a friendly pawn) is generally considered to be worse if it is (a) on a half-open file (no enemy pawn in front of it AND (b) the enemy has rooks to attack it.

IMHO, a pawn that is backward and unopposed is not any weaker or stronger than a backward pawn that is opposed, if there are no enemy rooks to contend with. Any backward pawn is weak, and inviting to enemy kings in the endgame. backward pawns on half-open files make inviting targets even in the middle game if you have rooks to attack on the file.

I've seen games decided by two types of backward pawns, repeatedly.

The first is the classic backward pawn on a half-open file, which is just as bad as an isolated pawn on a half-open file, when the enemy has rooks. Pile up on the pawn, tying up the opponent by making him defend, and either win the pawn outright, or switch to some other idea once he is tied down and not coordinated very well.

The second is a pawn that is backward, but the file is not half-open. If you have just one, you might manage to defend it with your king, depending on the position. If you have two, the enemy king can make you commit to saving one and then to eat the other pawn chain. Doesn't matter whether the file is half open or not.

[d]6k1/5p2/4p1p1/3p2P1/1p1P4/p7/P7/6K1 w - - 0 1

I tend to concur with Bob's definition. In the diagram above the e6 pawn is still defended, and thus not vulnerable to direct attack, so that's an argument against calling it backward.

However, since it cannot safely advance, there is an element of backwardness about it, and the square in front of it (e5) can serve as a good outpost for White pieces. These considerations should justify some sort of a penalty for such a pawn, but a lesser one that a fully backward [undefendable by a fellow pawn] pawn on an open file.

The Black b-pawn, even though backward, could be pushed in some cases creating a dangerous advanced passed pawn. It's not as clear whether a backward pawn that sits in the opponent's half of the board deserves any significant penalty.

CL

[Ferdy]

My take on this is that you are somewhat mixing terms.

A pawn that is defended by a pawn is not considered backward in any book I have (g6 in your first example as it is defended by h7). The fact that it can not safely advance is not so important when it is perfectly safe where it is. If you want to talk about it being immobile, that is a different issue.

the "unopposed" requirement stems from the rook, in the books I have read over the years. A pawn that is backward (can not be safely defended by a friendly pawn) is generally considered to be worse if it is (a) on a half-open file (no enemy pawn in front of it AND (b) the enemy has rooks to attack it.

IMHO, a pawn that is backward and unopposed is not any weaker or stronger than a backward pawn that is opposed, if there are no enemy rooks to contend with. Any backward pawn is weak, and inviting to enemy kings in the endgame. backward pawns on half-open files make inviting targets even in the middle game if you have rooks to attack on the file.

I've seen games decided by two types of backward pawns, repeatedly.

The first is the classic backward pawn on a half-open file, which is just as bad as an isolated pawn on a half-open file, when the enemy has rooks. Pile up on the pawn, tying up the opponent by making him defend, and either win the pawn outright, or switch to some other idea once he is tied down and not coordinated very well.

The second is a pawn that is backward, but the file is not half-open. If you have just one, you might manage to defend it with your king, depending on the position. If you have two, the enemy king can make you commit to saving one and then to eat the other pawn chain. Doesn't matter whether the file is half open or not.

[d]6k1/5p2/4p1p1/3p2P1/1p1P4/p7/P7/6K1 w - - 0 1

I tend to concur with Bob's definition. In the diagram above the e6 pawn is still defended, and thus not vulnerable to direct attack, so that's an argument against calling it backward.

However, since it cannot safely advance, there is an element of backwardness about it, and the square in front of it (e5) can serve as a good outpost for White pieces. These considerations should justify some sort of a penalty for such a pawn, but a lesser one that a fully backward [undefendable by a fellow pawn] pawn on an open file.

The Black b-pawn, even though backward, could be pushed in some cases creating a dangerous advanced passed pawn. It's not as clear whether a backward pawn that sits in the opponent's half of the board deserves any significant penalty.

CL

I believe that Hans deeply thought that one of the major qualifiers for backward was for that pawn to be still in the lower ranks (2nd and 3rd). The ideal rank for most pawn is at 4th. If it is on 5th, and beyond, we might labelled it as over extended. It is even possible that a pawn in the 2nd and 3rd rank will get more penalty (aside from the pst) as game progresses, no need to calculate if its stop (a square in front) is attacked or not.

[Lyudmil Tsvetkov]

Last time I checked the definition of "backward pawn", an "isolated pawn" that was not a "passed pawn" is backward too ...

[d]6k1/8/2p5/8/p7/2P5/1P6/6K1 w - - 0 1
You want to say a4 and c6 are backward too?

Yes. Neither can be defended by friendly pawns. backward is just a special case of isolated, or vice versa. Both are weak. I only evaluate "weak" pawns in Crafty, for example. There are various levels of "weak" to be sure (white pawns on c5/e5, black pawns on c4 and d3. That d3 pawn is REALLY weak. Remove either the c5 or e5 pawn and it is not so weak as a piece can help it advance and liquidate. But with both c5/e5 the d3 pawn simply can not move, period.

It is mainly because of periods that moern engines play so poorly with their backward pawns. That they fail to capitalise on a potential for improvement in this particular field that is worth 30-50 elo.

[Lyudmil Tsvetkov]

[d]6k1/3p4/1p6/p3p1p1/P3P2p/1P1P3P/6P1/6K1 w - - 0 1
I consider b3, d3 and g2 as backward for white. The engine will strive to remove this bacward pawn by supporting the push by pieces. For example white will play b4, if axb4 and a white piece takes b4 too, what we have now is a black backward pawn in b6, the white a4 pawn is not backward because it is already in the fourth rank. So black will prepare something if ever white will achieve the push, because if black will not take the white's b4 pawn push, white has the posibility now of either moving b4b5 grabbing space or b4xa5.

[d]6k1/3p4/1p6/4p1p1/P3P2p/3P3P/6P1/6K1 w - - 0 1
So why on Earth b6 should be backward and a4 not? Those pawns already get different psqt values for 4th and 3rd rank respectively, but apart from that, what is the difference between them? They both can not advance, it is 1 vs 1, some bonus for pawn control only for a4 is OK, but that would be 5-8cps, we are talking here of giving 20-30cps and more penalty for a real backward pawn. Is it possible that b6 gets penalised so much?

And also why d3 is backward? It can not advance, but black's d pawn also can not advance past the 6th rank, and it is an equal distribution of resources, 2 vs 2, neither side gets anything special from that situation. So that I think, although d3 could be penalised, this is wrong in practical terms.

To ask you one question, Ferdinand, how is Deuterium able to play so strong when it understands backward pawns so poorly?

There is a book "Pawn Power in Chess" by Hans Kmoch that says a backward pawn is a half-free pawn on the 2nd or 3rd rank whose stop square lacks pawn protection but is controled by a sentry. I generally coded in this way. Tuning these values is certainly possible. Still there are a lot to change and tune, the state of the affair is to minimize the bugs

So it is mainly Kmoch to blame that engines generally play so poorly with backward pawns.

Do not you get it Ferdinand, all pawns above cancel each other, there is simply no reason at all to implement them. Those are not real backward pawns. A real backward pawn is only the case when 1 pawn stops 2 enemy ones by attacking the stop square of one of them and blocking the other. Such pawns do not cancel each other and it makes much sense to implement them and elaborate on them.

[Lyudmil Tsvetkov]

[d]6k1/3p4/1p6/p3p1p1/P3P2p/1P1P3P/6P1/6K1 w - - 0 1
I consider b3, d3 and g2 as backward for white. The engine will strive to remove this bacward pawn by supporting the push by pieces. For example white will play b4, if axb4 and a white piece takes b4 too, what we have now is a black backward pawn in b6, the white a4 pawn is not backward because it is already in the fourth rank. So black will prepare something if ever white will achieve the push, because if black will not take the white's b4 pawn push, white has the posibility now of either moving b4b5 grabbing space or b4xa5.

[d]6k1/3p4/1p6/4p1p1/P3P2p/3P3P/6P1/6K1 w - - 0 1
So why on Earth b6 should be backward and a4 not? Those pawns already get different psqt values for 4th and 3rd rank respectively, but apart from that, what is the difference between them? They both can not advance, it is 1 vs 1, some bonus for pawn control only for a4 is OK, but that would be 5-8cps, we are talking here of giving 20-30cps and more penalty for a real backward pawn. Is it possible that b6 gets penalised so much?

And also why d3 is backward? It can not advance, but black's d pawn also can not advance past the 6th rank, and it is an equal distribution of resources, 2 vs 2, neither side gets anything special from that situation. So that I think, although d3 could be penalised, this is wrong in practical terms.

To ask you one question, Ferdinand, how is Deuterium able to play so strong when it understands backward pawns so poorly?

Think like a computer. d6 is a "weakly backward pawn", As is d3. We call that a "wash". So no side has any advantage there. If one side has more of those weak pawns than the other, they then become a real disadvantage.

What is the purpose of considering terms that cancel each other and have no real contribution to evaluation?

[Lyudmil Tsvetkov]

My take on this is that you are somewhat mixing terms.

A pawn that is defended by a pawn is not considered backward in any book I have (g6 in your first example as it is defended by h7). The fact that it can not safely advance is not so important when it is perfectly safe where it is. If you want to talk about it being immobile, that is a different issue.

the "unopposed" requirement stems from the rook, in the books I have read over the years. A pawn that is backward (can not be safely defended by a friendly pawn) is generally considered to be worse if it is (a) on a half-open file (no enemy pawn in front of it AND (b) the enemy has rooks to attack it.

IMHO, a pawn that is backward and unopposed is not any weaker or stronger than a backward pawn that is opposed, if there are no enemy rooks to contend with. Any backward pawn is weak, and inviting to enemy kings in the endgame. backward pawns on half-open files make inviting targets even in the middle game if you have rooks to attack on the file.

I've seen games decided by two types of backward pawns, repeatedly.

The first is the classic backward pawn on a half-open file, which is just as bad as an isolated pawn on a half-open file, when the enemy has rooks. Pile up on the pawn, tying up the opponent by making him defend, and either win the pawn outright, or switch to some other idea once he is tied down and not coordinated very well.

The second is a pawn that is backward, but the file is not half-open. If you have just one, you might manage to defend it with your king, depending on the position. If you have two, the enemy king can make you commit to saving one and then to eat the other pawn chain. Doesn't matter whether the file is half open or not.

Who is mixing terms, me who have a single definition for a backward pawn, or you and other engine authors who define backward pawn as 'weak, isolated, overextended, undefended' at the same time? And even worse, apply those absolutely unclear and polluting definitions to their engines.

The meaning of the word backward is underdeveloped, unable to advance. So that a backward pawn basically is a pawn that is unable to advance, if we have to apply the definition across ranks. As you need efficiency in order to apply a concept, a backward pawn is strictly the case when 1 pawn stops 2 enemy ones by blocking one and attacking the stop square of the other. No other definition possible, if you need to introduce at least a somewhat reasonable term valid across ranks.

And it does not matter that someone wrote something somewhere, it is just not like that. Do you believe all the books you read?