We have come to the last part of my series on the positional exchange sacrifice (see also part 1 and part 2). By no means have we covered all possible reasons to sacrifice the exchange - were I to try to do that, the series would go on for many articles. It is time to move on. But we will have covered three very important justifications for a positional exchange sacrifice.
This week we will be looking at perhaps the most common reason for an exchange sacrifice - to remove an important enemy bishop. In chess, the presence - or absence - of bishops of certain colors have a huge effect on the overall health of the position. The bishop is sort of like the spiritual guardian of its color of squares. Thus, in certain positions, it can pay dividends to sacrifice a rook for a particularly important bishop.
The first example is a well-known exchange sacrifice right in the opening made by Garry Kasparov. At the time, his purely-positional and long-term sacrifice was very surprising.
The great Garry Kasparov
A lot of exchange sacrifices are connected to a fianchettoed bishop - either a sacrifice to eliminate the opposing fianchettoed bishop, or a sacrifice to make one's own fianchettoed bishop very powerful, by eliminating its opposite at the cost of a rook.
Here is an example of the first case - from a seemingly placid position, Ulf Andersson makes a positional sacrifice of a rook for his opponent's fianchettoed bishop. There is no concrete variation to back up the sacrifice; only intuition.
The legendary Ulf Andersson (Sweden) | Photo Wikipedia
And here is the flip side of it - a sacrifice of an exchange for the fianchettoed bishop's opposite number:
In this typical Benoni position, the black fianchettoed bishop is very important. The strange position of the white bishop on e3 gave Topalov the opportunity to sacrifice the exchange to gain control of the dark squares by 15...Rxe3! 16.fxe3 Nf6. In addition to capturing White's important dark-squared bishop (thus making his own dark-squared bishop very powerful) Black has severely weakened White's pawn structure. As a result Black gains a base of operations on e5 and the chance to attack the weak pawns. In the subsequent play, it was shown that Black's position had all the dynamics.
Finally, here is a typical example of a sacrifice of the exchange to remove White's dark-squared bishop. In the resulting position Black gains iron control of the dark squares, and we have a sort of combination of today's theme and that of last week (blockade):
The three themes which we have covered have of course not covered all of the possible reasons for exchange sacrifices. For example, one common justification for an exchange sacrifice is to ruin the opponent's pawn structure. In some of the examples I have used, this was an auxiliary factor.
However, I have focused on the concept that - when you sacrifice the exchange - you are losing one piece and gaining another. Thus you don't really have less pieces than your opponent - you just have different ones, of a different level of "quality" (which is what the "exchange" is called in most languages). Usually the rook is the stronger piece, but in some positions it is the minor piece which shows the greater strength, often for long periods of time. The difficulty lies in assessing whether the position is such, and how long it will remain that way. The main point is that the material values are not etched in stone, but merely an average based on human experience, and sometimes these well-known values can be overturned.