09 Oct '07 23:42>
Originally posted by RagnorakYes, the reason why the bishop pair is worth about a half pawn (based on the study linked earlier) bonus is that the bishops don't duplicate each other's coverage. Any other combination of pieces gives you some duplication of coverage, which diminishes the value of the combo. So, in reality, the bishop pair isn't worth more; the other combos are worth a little less. But it's easier to think of the bishop pair as worth more.
coquette
"but two bishops or two knights are worth more than a bishop and knight together because the pieces "work better" together"
Rubbish! If there was only your opponents king against your two minor pieces, are you saying you'd want the two knights? With which you can't (forcibly) checkmate your opponent.[/b]
Quoting the article: "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."
Also: "The conclusions are clear and consistent: although the average value of a bishop is noticeably higher than the average value value of a knight, this difference is entirely due to the large value of the bishop pair. In other words, an unpaired bishop and knight are of equal value (within 1/50 of a pawn, statistically meaningless), so positional considerations (such as open or closed position, good or bad bishop, etc.) will decide which piece is better."