Bishop and knight comparison

Hi,

In the exchanges between knights and bishops the position of each piece is important. But is there any simple rule that can show in each condition (start of game, endgame, queens exist/dont exist, etc) what piece between knight and bishop is usually more valuable?

It's fun to compare the knight and bishop.

At first the bishop looks to be nothing more than a tall pawn... but it is so much more!  Instead of a boring ball, it has a cool hat.  This hat has a slit in it that makes it better than any hat I've ever seen.

The knight though it even better, and probably the most intricate piece.  It has a whole horses head on it, complete with mane, eyes, and sometimes even individual teeth!

I often exchange minor pieces (bishops and knights) but I like my knights because they just look so cool.  Bishops are pretty sneaky though, hiding out on those long diagonals when they go hunting for rooks.

To answer seriously though, there's no simple rule to show you which is better in any given situation.

The more active piece is the better piece. 

If you want a general rule, in general knights are more valuable the more pawns are on the board.  The more pawns on the board means pieces can get crowded and knights are the only piece that can jump over other pieces.

As more pawns come off, the board is more open, which highlights the bishop's strength.  So often in endgames a bishop will be stronger than a knight when pawns are on both sides of the board.

This brings us back to activity, which is the only real way to judge between two pieces.  When pawns are only on one side of the board in an endgame, a bishop may not be nearly as useful because it can only ever affect half of the squares! (light square bishop is stuck on light squares).

In the middle game you can check for activity by seeing if a bishop is on an open or long diagonal pointing towards important squares such as a castled king, the center, or an enemy weakness.

Knights like outposts which are squares protected by a friendly pawn.  A strong outpost means an enemy pawn can never attack that square.

Finally when trying to decide whether or not to trade pieces, be sure to look at the pieces left on the board, not necessarily the pieces that are coming off.  For example you may be exchanging a not so active bishop for a well placed knight, but if your remaining army is poorly placed, then it's likely you made a mistake.

I have heard that the average value of bishop is about 3 pawns while for knight it is 2.5 pawns. Is it true?

sometimes we have two exchanges and two minor piece remain for each side.

What pair of these pieces is usually better? knight-bishop, bishop-bishop (against knight-knight), knight-knight (against bishop-bishop)

The knight by itself is worth 3 and the bishop by itself is worth 3.  They even did some computer analysis of the piece values and the computer came up with bishop and knight values as equal (to within 1/50th of a pawn).  Source: http://home.comcast.net/~danheisman/Articles/evaluation_of_material_imbalance.htm

As for pairs of piece, knight-knight, and bishop-knight are equal.  It really depends on what the rest of the board looks like.  You know... if you have one knight that is stuck in a corner, then it's bad :)

Bishop-bishop is the only pair that has a special value given to it.  If you have the bishop pair then it's sometimes worth half a pawn.  Two bishops are sometimes better than knight-knight or bishop-knight, especially if it's an open position like many endgames are.

Still, I have to repete that it depends on the position.  Sometimes knight-knight is very strong and just what a player needs.

Thanks for the valuable information