# Chess Opening Theory
## What is opening theory?

So, you've learned the rules of chess. You've learned that moving your bishops and knights off the back row and controlling territory is a good plan, and letting lots of your pieces get captured for free is a bad one. (If you have doubts about any of that, head over to the Chess Wikibook first!)
Now it's time to answer that $64,000 question that's on the tip of every new chess player's tongue. The question that cuts right to the heart of what it means to be a competitive board game player:
   How can I beat my friend in, like, four moves?

### Beating your friend in four moves

Yes, it is possible! But only if your friend doesn't see it coming. Otherwise we'd have solved chess, and no one would play it.
If you're playing as White, then the trick is to carry out a lightning attack on the weak f7-pawn. It's a weak pawn because it's defended only by the black king. If you can attack it with two pieces while it's defended by only one, you've won it for free. If you're playing as Black, then you can try for something similar by attacking White's f2-pawn. Let's look at how White can perform this trick.
White's first move is 1. e4. The queen and f1-bishop, which were stuck on the back rank, can now be developed. Developing a piece means moving it off the back rank and putting it somewhere more useful. The plan is to quickly develop the queen and f1-bishop in such a way that they both attack the f7-pawn.
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Black replies by copying White: 1...e5.
Then, White brings out the f1-bishop, as planned: 2. Bc4. Notice how it attacks the weak f7-pawn. It's now got one attacker and one defender.
Black isn't entirely sure what's going on, and so copies White again: 2...Bc5.
White makes a bold queen move: 3. Qh5. That's two attackers on f7, and still only one defender.
Black notices that the queen on h5 is threatening the pawn on e5, and so defends it with the innocent 3...Nc6?? (diagram A).
White plays 4. Qxf7#. The # stands for checkmate. Oops!
What did Black do wrong here? Let's allow Black to take back the move 3...Nc6 and replace it with 3...Qe7! (or 3...Qf6!) which defends the f7- and e5-pawns simultaneously (diagram B). Now, what does White's queen think she's doing on h5? Everything she can attack is defended. She can't make any more progress. If she was a hockey player, she would be offside.
But more importantly, Black is going to play ...Nf6 next and gain a tempo on the queen.
Gain a what?

## Tempos, and the gaining of them

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Chess is a turn-based game, but an unusual one: you can only move one piece each turn except when castling. If your queen is doing something this turn, bad luck, the rest of your pieces have to stay put. In business-speak, there's an opportunity cost to moving the queen.
Each turn is a precious commodity, which we call a tempo (Italian for 'time'). A tempo is an opportunity to move something.
Doesn't black always get one tempo for every tempo white gets? Not quite.
If your queen gets attacked by a knight, you've got to move it or lose it. Instead of developing another piece, you've got to waste this tempo re-locating a piece you'd already developed. So black's move ...Nf6 is basically a free action. Chess players would say "Black has gained a tempo on the queen".
And that right there is opening theory in microcosm. In the opening, developing your pieces is everything. To develop your pieces, you need tempos. How do I develop my pieces so that I don't lose any tempos along the way, and if possible I gain tempos at my opponent's expense? The answer to that question is Chess Opening Theory.
The perfect chess opening is one where you develop every piece in a single move to its best possible square, and then leave it there. (Lots of players have searched for the perfect chess opening. Sadly, every one has its own drawbacks.)
Things like space (controlling lots of squares with your pieces), structure (keeping your pieces and pawns supporting each other) and even material (how many pieces you've got left on the board) can all take a back seat. If you want to know the real reason the grandmasters are playing one opening move instead of another, think development, and think tempos. Or if you're pedantic, think tempi.

## White's first move

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### King's Pawn Opening

The move 1. e4, called the King's Pawn Opening, is the most popular initial move at every level of chess from beginner to grandmaster. Even if you aren't trying to checkmate black in four moves, letting both the queen and the king’s bishop out is a good thing to do.
You might hear people recommending 1. e4 because it controls the important central squares d5 and f5, which is true. However, the most important square white controls by playing 1. e4 is in fact... the e4 square itself. Having a white pawn on that square means there won’t be a black pawn on that square anytime soon, which means that the king’s knight can be developed to f3 without fear of getting kicked by a pawn and losing a tempo.
And just as white indirectly claims the f3 square by playing e4, Black has to bear in mind that f6 will not be a safe square for the g8 knight if White can simply advance the pawn to e5. The simplest way for Black to fix this problem would be to copy White and play 1...e5 in response.
So why would you ever play anything other than 1. e4 - and why would Black ever meet it with anything other than ...e5? It took chess players a few hundred years to realise the answer to that question:
If Black wants to play ...e5, but instead of 1. e4 I play a move that attacks the e5 square, Black can't play ...e5 anymore!
And so they invented:

### Queen's Pawn Opening

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1. d4 is called the Queen's Pawn Opening. It is the 2nd most popular initial move (at all levels) and is in the same ballpark as 1. e4 in terms of games played. All the other legal moves combined appear in about half as many games as 1. d4. If chess opening theory is a solar system you have Planet 1. e4, Planet 1. d4, a few dwarf planets and some dust.
1. d4 is played to prevent Black from getting the useful move ...e5 in straight away, while also controlling the c5-square. It discourages Black from developing the b8 knight to c6, where the pawn can advance to d5 and kick it, though this is nevertheless occasionally seen.
White isn't necessarily interested in developing their queen’s bishop straight away - it tends to be the least important piece to develop. 1. d4 is more about slowing down Black's development than speeding up White's.
If Black retaliates in kind with 1...d5 to prevent White from following up with 2. e4, White can instead play 2. c4, the Queen's Gambit, hoping to divert Black's pawn from its job of attacking e4. The Queen's Gambit is the champagne and caviar of White openings and is a huge reason for the popularity of 1. d4.
A note on the word gambit: a gambit is a specific kind of opening in which material (pawns or, rarely, larger pieces) is sacrificed to gain some form of dynamic advantage (speedy development, an attack, extra tempi, etc.). Always think development and tempi! If there's no material sacrificed, it's not a gambit. "Opening gambit" is a tautology. Despite what the musical CHESS may have told you, not every opening is a gambit!

### How do I choose between 1. e4 and 1. d4?

Conventional wisdom says that if Black’s position were a castle, 1. d4 players prefer to capture it by digging under the foundations, whereas 1. e4 players like to crash through the front gate on a flaming motorcycle.
This is a bit of an over-generalisation. You're not going to get put into a four-move checkmate by a 1. d4 player, but if you play bad moves you'll still get wiped out. Read Irving Chernyev's instructional books, or the collected games of the great inter-war players Lasker, Capablanca and Alekhine, and you'll soon discover how easy it is to get hit by a tactical avalanche while playing a "strategic" Queen's Gambit.

### Other opening moves

In the chess opening theory solar system, alongside planets e4 and d4, there are a few other dwarf planets of note.
* 1. Nf3, the Zukertort Opening (sometimes referred to as the Réti Opening, or the King’s Indian Attack), is the 3rd most popular initial move. It's a sophisticated way of stalling for time, and waiting to see what Black tries before transposing into a more mainstream opening. White reckons that Nf3 will almost certainly be a useful move sooner or later, whereas every pawn move is an irrevocable commitment. 1. Nf3 also has the benefit of cutting out the reply 1...e5 by Black, which is a move that Black likes to play for all the same reasons that White likes to play 1. e4. 1. Nf3, as stated previously, can transpose into so many openings and is very flexible.
* 1. c4, the English Opening, is the 4th most popular move. White frees the queen, discourages the move 1...d5 by taking control of that square, and makes absolutely sure that the c-pawn won't get stuck on c2 behind a knight on c3. The resulting positions have more of a 1. d4 character than an 1. e4 character, and indeed the move d4 often follows later.
* 1. g3, the Benko Opening, is the 5th most popular initial move. It doesn't immediately influence the centre, but White plans to follow up with Bg2 which does. The hypermodern school of opening theory, most influential in the 1920s and 1930s, was all about controlling the centre from a distance with pieces rather than occupying it with pawns.
* 1. b3 is the Nimzowitsch-Larsen Attack (or Larsen's Opening), a hypermodern idea akin to 1. g3. Instead of preparing to castle kingside, White tries to scare Black out of it by pointing a bishop at g7.
* 1. f4 is the Bird's Opening, a risky and agressive opening that has the same idea as the English but on the kingside. However, it does not actually prevent 1...e5. 1.f4 e5 is the well-known (and generally sound) From Gambit, which contains a fiendish trap for an unwary White player. 1. f4 also weakens White's kingside slightly.
* 1. Nc3 is the Dunst Opening. There are many possible transpositions after 1. Nc3. A transposition just means playing the same moves in a different order. Where a position A is most commonly reached through opening B, it will be classified under opening B. If you reach it through opening C, you will have transposed from opening C to opening B. For example, 1. Nc3 e5 2. e4 is a transposition to the Vienna Game because the standard Vienna Game move order is 1. e4 e5 2. Nc3.
* 1. b4 is the Polish Opening. White reckons Larsen's opening can be improved upon by moving the pawn further forward. The pawn controls more space on b4 instead of b3, but is more vulnerable, and the space it controls is not space that typically needs to be controlled. It is still a completely playable move. This is a sort of fashionably eccentric opening for people who wear bow ties.

### All possible initial moves

| Quick Navigation | a4 a3 Na3 | b4 b3 | c4 c3 Nc3 | d4 d3 | e4 e3 | f4 f3 Nf3 | g4 g3 | h4 h3 Nh3 |

### Encyclopaedia of Chess Openings

    ECO volume A : English Opening, Benoni Defence, Dutch Defense, King's Indian Attack, Benko Gambit, Old Indian Defense, Bird's Opening, other so-called irregular openings
    ECO volume B : Sicilian Defence, Caro-Kann Defence, Pirc Defence, Modern Defence, Alekhine's Defence, Scandinavian Defence
    ECO volume C : Ruy Lopez, French Defence, Petrov's Defence, King's Gambit, Philidor Defence, Giuoco Piano, Two Knights Defence, Scotch Game
    ECO volume D : Queen's Gambit Declined, Queen's Gambit Accepted, Slav Defence, Tarrasch Defence, Grünfeld Defence, Queen's Pawn Game
    ECO volume E : Nimzo-Indian Defence, Queen's Indian Defence, King's Indian Defence, Catalan Opening, Bogo-Indian Defence

### Statistics

Approximate chances: White win 39%, Draw 32%, Black win 29%
Estimated first half-move popularity: e4 49%, d4 33%, Nf3 8%, c4 6%, g3 1%, b3 1%, f4 1%, all other moves less than 0.5%.
| Half-move | Average | 365Chess.com (big) | Chess Tempo (all) | chessgames.com | Lichess (masters) | Lichess (database) |
| e4 | 48.6% | 49.4 | 47.9 | 46.7 | 45.2 | 54.1 |
| d4 | 32.9 | 32.7 | 34.0 | 35.1 | 36.1 | 26.7 |
| Nf3 | 8.4 | 8.6 | 9.0 | 9.3 | 10.1 | 4.8 |
| c4 | 6.4 | 6.9 | 6.8 | 7.2 | 6.9 | 4.0 |
| g3 | 1.0 | 0.7 | 0.7 | 0.6 | 0.8 | 2.1 |
| b3 | 0.7 | 0.4 | 0.6 | 0.4 | 0.4 | 1.9 |
| f4 | 0.5 | 0.6 | 0.5 | 0.4 | 0.2 | 1.1 |
| e3 | 0.4 | 0.1 | 0.1 | 0.0 | 0.0 | 2.0 |
| Nc3 | 0.3 | 0.2 | 0.2 | 0.1 | 0.1 | 0.7 |
| d3 | 0.2 | 0.1 | 0.1 | 0.0 | 0.0 | 1.1 |
| b4 | 0.2 | 0.2 | 0.2 | 0.1 | 0.1 | 0.5 |
| c3 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.4 |
| g4 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.3 |
| everything else | 0.1 | 0.1 | 0.1 | 0.0 | 0.0 | 0.5 |
One might also be curious about the most frequent initial sequences in chess for both White and Black. Below are the first twenty-five most common beginnings.
Popularity of Top 25 Full Moves :
| Move | Popularity | Variation |
| 1. e4 c5 | 19.0% | Sicilian Defense |
| 1. d4 Nf6 | 17.1 | Indian Game |
| 1. e4 e5 | 12.6 | Open Game |
| 1. d4 d5 | 9.4 | Closed Game (Queen's Gambit, etc.) |
| 1. e4 e6 | 6.0 | French Defense |
| 1. e4 c6 | 3.8 | Caro-Kann Defense |
| 1. Nf3 Nf6 | 3.4 | flexible (including Queen's Pawn or English systems) |
| 1. Nf3 d5 | 2.3 | flexible (King's Indian Attack, Queen's Gambit, Réti, etc.) |
| 1. e4 d5 | 2.0 | Scandinavian Defense |
| 1. e4 d6 | 1.9 | Pirc Defense |
| 1. d4 e6 | 1.8 | the flexible Horwitz (Queen's Pawn, French, etc.) |
| 1. c4 Nf6 | 1.8 | Anglo-Indian Defense |
| 1. e4 g6 | 1.5 | Modern (Robatsch) Defense |
| 1. c4 e5 | 1.5 | Reversed Sicilian |
| 1. d4 g6 | 1.0 | Modern Defense (Queen’s Pawn) |
| 1. e4 Nf6 | 1.0 | Alekhine Defense |
| 1. d4 d6 | 1.0 | flexible (Modern, Pirc, King's Indian, Old Indian) |
| 1. Nf3 c5 | 0.9 | Sicilian, Réti |
| 1. d4 f5 | 0.9 | Dutch Defense |
| 1. c4 e6 | 0.9 | English |
| 1. c4 c5 | 0.7 | Symmetrical English |
| 1. d4 c5 | 0.7 | Old Benoni Defense |
| 1. c4 g6 | 0.5 | English Great Snake |
| 1. c4 c6 | 0.5 | English, Caro-Kann, Slav, or Réti |
| 1. Nf3 g6 | 0.5 | Réti |
| everything else | 7.2 | |

## Using this wikibook

Each page in this Wikibook corresponds to a single position, which will be shown in the diagram on that page. You are currently looking at the page for the initial position - the way the pieces are laid out when you first set them up on the board. One or more links will appear in the main body of the text, like this one: 1. e4. These represent possible moves from that position. Choose a move, click it, and reach a new position. Sometimes a list of common moves will appear under the page diagram, and if you find reading words about chess positions boring, you can pick the next move from that list too.
You can use the Encyclopedia of Chess Openings (ECO) code index if you prefer to navigate to positions that way.
Head over to the Great Big Opening Survey page to see a list of the opening lines that this Wikibook ought to be covering if it isn't already. Please help add the ones that are missing!
When contributing to this Wikibook, please follow the conventions for organization.
To find a certain chess position in this Wikibook, paste the first field of the position's FEN record into the box below and wrap it inside quotation marks. Try e.g. "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR".

## Theory table

For explanation of theory tables, see theory table and for notation, see algebraic notation.
| | 1 | 2 | 3 | 4 | 5 | 6 | Evaluation |
| Sicilian Defence | e4 c5 | Nf3 d6 | d4 cxd4 | Nxd4 Nf6 | Nc3 a6 | Be3 e5 | +/= |
| Ruy Lopez | e4 e5 | Nf3 Nc6 | Bb5 a6 | Ba4 Nf6 | O-O Be7 | Re1 b5 | +/= |
| King's Indian Defence | d4 Nf6 | c4 g6 | Nc3 Bg7 | e4 d6 | Nf3 O-O | Be2 e5 | +/= |
| Queen's Gambit Declined | d4 d5 | c4 e6 | Nc3 Nf6 | Bg5 Be7 | e3 O-O | Nf3 Nbd7 | +/= |
| King's Indian Attack | Nf3 d5 | g3 Nf6 | Bg2 c6 | O-O Bg4 | d3 Nbd7 | Nbd2 e5 | = |

## Notes

* ↑ Technically, the Queen’s Gambit Accepted and a form of the London System were already conceived in the Göttingen manuscript.
* ↑ 1. d4 e5 is a real opening (the Englund Gambit), but it is considered unsound.
* ↑ 1. d4 d5 2. e4 is also a real opening (the Blackmar-Diemer Gambit), but a notoriously risky one.
* ↑ Nf3 e5 technically an opening, but it's considered to be even worse than 1. d4 e5 or 1. d4 d5 2. e4, so don't play it.

## References

* Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.
* Modern Chess Openings: MCO-14. 1999. Nick de Firmian, Walter Korn. ISBN 0-8129-3084-3.
* Nunn's Chess Openings. 1999. John Nunn (Editor), Graham Burgess, John Emms, Joe Gallagher. ISBN 1-8574-4221-0.