why are the two bishops so good


In positions that are not too blocked-up by interlocked Pawns, the Two Bishops are an advantage for several reasons.
a) a properly-placed Bishop can influence the play on two widely-separated parts of the chess-board... center and Q-side, for example, or to defend on one flank while attacking on the other. It's very difficult to safely position a Knight to do this.
b) a Bishop does not need to be close to its target in order to attack it... a Bishop on g2 can threaten the a8-Rook, for instance. Knights must first approach their target before they can threaten it. You can hear a Knight coming (thud-thud-thud), but not a Bishop (SWOOSH!).
c) it is mechanically easier to arrange to trade your Bishop for an opposing Knight than vice-versa. This means that it is the player with the Two Bishops who usually has the option to simplify into an endgame.

If you ever get stuck in a basic endgame with only a bishop and a knight against a lone king, you'll definitely wish that knight were a bishop.
There are positions where two knights or a knight and bishop dominate the two bishops. A player should not be dogmatic of wanting the bishop pair all the time. He must know that certain situations will be a disadvantage for him if he tries to hang with the bishop pair. A sample situation of this is you might get too behind in development just to preserve your bishop pair. The position is too closed for your bishop pair to flourish. But many positions favors the two bishop. They are powerful duo because they cover both colors. You also have option of exchanging one of them under favorable circumstances.
To get better understanding on when having two bishops favors you or not, you must look at various games and study books.
There are many games that demonstrate the power of two bishops. Take a look at these.
Topalov and the two bishops
http://www.chessgames.com/perl/chesscollection?cid=1005826
http://www.chessgames.com/perl/chessgame?gid=1132616
Bishop pair + passed pawns = winning equation
http://www.chessgames.com/perl/chesscollection?cid=1010447
The bishop pair
http://www.chessgames.com/perl/chesscollection?cid=1007957
Fabiano Caruana and the Bishop Pair
http://www.chessgames.com/perl/chesscollection?cid=1024216
Kasparov,Kramnik,Fischer etc have many brilliant games using their bishop pair.
Not true. Most of the time, two bishops are better.

Hi, I would say that while the B vs N debate is less clear, the B pair is almost always better than 2 N. One of the reasons being that it is generally easier to bring about positions that favor Bishops.
Ok people, lets hit the bottom line: 2 knights can't create a forced mate. 2 bishops can. 2 bishops are better. end of story.
Am by no means an expert, but I prefer a bishop over a knight in the same way I would prefer a gun over a knife. Both are lethal but you need proximity to you target for a knife to be useful. A Bishop is a long range weapon. You can put a bishop on one end of the board and it controls the entire diagonal.
A knight controls a lot of squares, but only within a close proximity.
Besides the biggest advantage is that even if a Bishop moves, it can still control a particular square. Which is especially a big advantage in end games. If you protect a particular square with a knight and that knight gets kicked or attacked then you are sure going to lose control of the square.
In the middle game when there are lots of pieces on the board, then a knight sometimes is more effective than a bishop, as it can hop around and control a lot of central squares. However as the board opens up and you head towards end games, Bishops I feel have an advantage over the knights.

because you can control two diagonals
or you can go to mass in the morning and attend again in the evening

You can use your two bishops to mine earwax out of both ears, or boogers out of both nostrils, at the same time. No other chess piece comes close in utility.
