The essense of chess tactics is to make a single move which threatens the opponent twice - unless they have some counter tactic to either deal with both threats, they will end up in a worse position, because you will be able to follow through on one of your threats with no trouble.
The simplest tactic is the fork - where one piece directly attacks two or more pieces. This is normally done by knights, because of their unique movement, but any piece may fork - including the king!
Other tactics include the following:
- Pin - A bishop, rook, or queen gets in line with two of the opponent's pieces, where the intermediary piece is less valuable than the one it is blocking. If the opponent moves the intermediary piece, the farther one can be captured. If the far piece is a King, it's called an absolute pin, because the intermediary piece cannot be moved.
- Skewer - Similar to a pin, but the intermediary piece is the more valuable one, and the opponent usually ends up having to move it, and loses the far piece.
- Discovered attack - By moving one piece out of the way, exposing a piece behind it so that it can attack another. The attacking piece can be a bishop, rook, or queen - and if the moved piece also makes an attack, the defender has a difficult choice as to which threat to defend against.
- Double check - This is a type of discovered attack where both attacking pieces check the opponent's king, which forces the king to move, as it is impossible to block both checks in a single move.
- Undermining -By capturing a piece which is defending another, the opponent has to chose between recapturing the attacking piece, or defending their newly undefended piece.
- Overloading - By gicing a defending piece too many squares that it has to defend, it has to give up defending some of them. This can result in hung pieces and other bad situations for the defender.
- Interference - By moving a piece in between two long-range pieces that are defending eachother, the opponent is forced to either defend against the new threat that the interfering piece makes, or to defend the pieces that are no longer defending eachother.
- X-Ray Attack - A piece defends another through an opponent's piece - if the opponent captures one of them, the other can recapture. http://en.wikipedia.org/wiki/X-ray_(chess)
- Zwischenzug - A counter-tactic where a player makes an intermediary move which poses a more dangerous threat than their opponent's most recent attack. This is a way to get out of situations caused by tactics used against you. Usually the intermediary move has to create a check on the opponent's king, since they are then compulsed to defend against it.
- Zugzwang - A situation that comes up usually in endgames, where the opponent would rather pass their turn than move. Of course, you can't pass your turn in chess, so they are compulsed to move to a position worse than the one they are in.
Tactics like these can be strung together to form combinations. An example of this is known as a windmill - a series of checks and discovered checks where the attacker can pick off defending pieces on every other move, and the place their pieces in a better position at the end. This usually happens where the opponent's king becomes stuck in a place where it has only a couple squares to move to. A good example is in this game, starting on move 25 with a queen sacrifice to set up the windmill.
In chess, there are huge depositories of games past, which can be explored using powerful tool such as chess.com's Game Explorer. Using this web program you can play moves and see what the winning percentages are for each move that comes after it. There are over two million games in the database, all from master-level players. Many of the games in this database follow what are known as main lines - over half of those games have e4 as the starting move. For those unfamiliar with chess notation, this is moving the king's pawn two squares forward.
What use is a chess database? For one, it makes it easy to see what your future chances may be, and how popular each line of reasoning is. Because of this, most chess-playing engines use what's known as an opening books, a type of chess database, to improve their play during the beginning part of the game. Likewise, people playing correspondence chess often use chess databases to avoid making blunders, and to look ahead to see what their opponent (who also is using a database) might play.
If you follow through a couple of moves it's easy to find an opening sequence that has rarely been been played before at the master level - these are known as 'novelties' or 'theoretical novelties' in chess. Many of these novelties are weak moves, but there are countless undiscovered complexities in chess, and some chess players enjoy exploring this new territory. If you play one of these novelties, computer and human player alike will have to throw away their chess database as well - since there is no more data to be drawn upon!
The corresponding idea in game design is to use a sort of novelty, innovation, or new technology to differentiate one game from another. It would be interesting to be able to locate novelties in game design, in a similar way to how they are discovered in chess. Let's take a look at a hypothetical design database which allows people to explore different types of designs and see what other projects made similar decisions, if anyone had actually made that design decision before.
Instead of chess moves, this design database has a sequence of design decisions, starting with the most important, overarching themes of a project, with following decisions refining and polishing the overall design. A design sequence for chess could be like this, in order of importance to the game:
- Abstract Strategy Game
- Two Players
- Special 'King' piece is put in check to win the game
- Pieces capture the opponent's pieces by moving into them
- Each piece has a different type of movement (described here)
- Some special moves can be made (Pawns moving 2 squares, castling, en passant, pawn promotion)
- Board is 8x8
- Pieces start out arranged in a particular manner
The order is important, since you can make changes more easily to the later items without greatly affecting how chess feels and plays. An example of this kind of change was a variant developed by Bobby Fischer some time ago in order to combat the rote memorization of opening systems in chess. The variant is known as Chess960, where the arrangement of the back rank of pieces is randomized (with some restrictions) before the game. The result is a game which plays almost exactly like chess, but places more emphasis on creativity and talent, rather than memorization and preparation.
On the other hand, you could hardly alter the earlier elements without changing the feel of the game, though depending on how they are changed it could still be considered a chess variant. Shogi has differences in 4, 5, 6, and 8, though it's still recognizibly a type of chess - it's also called Japanese chess.
Let's take a look at another decision sequence:
- First Person Shooter
- One player or two players cooperatively
- Fighting against aliens
- Player has health and shields, the shields recharge
- Vehicles are used in combat by one or more players at a time
- Players can hold only two sets of weapons at a time
- Players can use grenades as long as their weapon only takes up one hand
- Special items can be found which are used to enhance the player or detract from enemies
It should be pretty apparant that this game is Halo, though you wouldn't be able to tell which one unless someone expanded the sequence with more and more finer points. Taking the assumptions that come along with being a FPS game (running, jumping, ducking, aiming, shooting) you can get a pretty good idea what is going on in the game and how the combat plays out. Compare it to Gears of War, which has a similar design, though it is an over-the-shoulder camera, and I would probably replace the vehical combat with an item about the cover system, since that is what's important about the combat. There are other small changes as well, regarding the weapons held, grenades, and special items - though these are farther down the list, and ultimately less important than the earlier ones.
Another interesting comparison would be the differences between checkers and chess. I'll leave that as an exercise to the reader (because I am a jerk).
In conclusion, I think it'd be neat to have a database of games listed in this design sequence format, so you can pick one or two early (large) decisions and see what kind of games show up in the filtered list, including stats such as their critical and financial success, detractions, and links to similar games that differ in a bigger decision rather than a smaller one.