Look at the checkmates on the previous pages and you can easily see what is meant by greater force. In all of them the poor king got clobbered by an enemy queen. In the first two, the fool opened up lines of attack for the enemy and closed off all retreat or blocking opportunities. In the third checkmate the triumphant queen swooped in with the help of a friendly bishop.
We know the queen is powerful, but just how powerful is she? And how strong are the other pieces and pawns in comparison? In order to compare them all, we need a measuring stick. So let's take the least powerful of all, the pawn, and use that as our measure. With that in mind, here are all the pieces listed in terms of their average power, expressed in terms of numbers of pawns:
Knight = 3½
Bishop = 3½
Rook = 5
Queen = 9
King = infinity
There are several things about this list that may appear surprising or obscure. For instance, how can anything be worth half a pawn? And what is that about infinity?
A rook is generally stronger than a minor piece (a bishop or a knight). This difference is about 1½ pawns’ worth, and is called the Exchange. This is not to be confused with the general term exchange, which refers to trading one piece for another. Thus you can exchange bishops, or exchange a queen for a rook and knight, but if you trade a rook for a knight you have given up the Exchange.
Sometimes this list is represented with the bishops and knights being worth only three pawns. This is not so far wrong, but we get messed up when we take three minor pieces and compare them to the queen. They are significantly stronger than her majesty. And a bishop and knight are generally a bit stronger than a rook and pawn. So the half-pawns are there to make it all come out a bit better.
It's hard to compare bishops and knights. Knights can cover the entire board eventually, while bishops can cover only half the squares. Yet bishops are long-range pieces and have a lot more immediate power than knights.
Sometimes a knight is better.
Sometimes a bishop is better.
But when you fight with two bishops against two knights or a bishop and a knight, it is usually better to have the bishops. Together they have the long-range power and can cover every square on the board.
White is poised to checkmate on g7. Note the power of both bishops.
It's almost unfair to have this much power.
King Equal to Infinity
But what about the king being equal to infinity? That is in the very nature of chess. You can't put a value on the king, since he is not subject to capture. Thus all the pieces and pawns together won't equal his importance. As for his power when there are not many pieces left later in a game, it is something on the order of four pawns.
Greater Force Generally Wins
Greater force generally wins against lesser force. But only generally. In a sacrifice, a player gives up some greater force in order to bring about a concentration of force in a particular area of the board. For an example of a sacrifice, look at the game from Chapter 6. At the end of the game, Morphy gave up his queen for the chance to produce a checkmate.
White plays 16. Qb8+!
It is important to remember that these measurements are averages only. Rooks are generally much stronger than pawns, but what about a pawn about to promote to a queen? Bishops are about equal with knights, but what about a bishop locked behind its own pawns with nowhere to go compared with a knight that can hop over the whole board with impunity?
You can think of each piece and its average power as a potential. As long as you keep this in mind, you won't go too far wrong when exchanging a piece for a supposedly less powerful piece that is doing a lot of damage.
Chess has good bishops and bad bishops. A good bishop is one with open diagonals, many places to go, and pieces and pawns to annoy.
The bishop gives White headaches on both sides of the board (a2 and h3).
A bad bishop is one that is trapped behind its own pawns. It doesn't have anything reasonable to do, and is sometimes referred to as a tall pawn, though sometimes even a pawn would be better. At least a pawn can move one square forward on a file.
The bishop has nowhere to go, and blocks the b8-rook as well.