Rules of Chess
Ole K. Christensen
1. Introduction
If you are not yet familiar with the rules of
chess, or you are just starting to play, you
can read the following tutorial. We will also
touch briefly on the basic usage of Sigma
Chess when needed.
Chess is a battle between two players called
White and Black. The game takes place on an
8x8 square board with 16 white and 16
black pieces, which are initially placed as
shown in the diagram.
White to move
White is leading (moving) the white pieces,
and Black is leading the black pieces. White
always makes the first move (i.e. moves one
of his own pieces). Then Black makes a
move, after which it's White's turn again
e.t.c.
A piece can move to an empty square but not
to a square that is already occupied by
another piece of the same colour. If a piece
moves to a square that is occupied by an
opponent piece, the opponent piece is said to
be "captured" and must be removed from the
board. Thus there can never be more than
one piece on a square.
- o O o -
HOW TO READ THIS TUTORIAL
This tutorial is a "game collection" designed
as an online chess book. It is divided into a
number of "sections", each of which either
contains text or an annotated chess game.
Once you have completed reading a section,
you can move on to the next section by
pressing Cmd-right arrow (which is a
shortcut to the "Next Game" command in the
"Collection" menu). If a section contains
moves (i.e. if the VCR style buttons > and >>
are enabled), you should replay these moves
first before moving on to the next section.
The text "[DIAGRAM]" on a single line
indicates that a diagram will be included of
the current board position when printing.
The collection windowshows a "table of
contents" of this online chess book showing
the titles of each section. You can move
directly to a section by double clicking on
the title in the list.
Press Cmd-right arrow to continue.
The Pieces
Before we can go into the details of how each
piece actually moves, we first need to get
acquainted with the various piece types: The
white piece in the lower lefthand corner
resembling a tower is called a "rook". Next
to the rook we find the horselike "knight",
followed by the "bishop", the "queen" and the
"king". Next to the king we then have one
more bishop, knight and rook. In front of
these 8 pieces on the second row are the 8
"pawns". Black is equipped with a similar
set of pieces.
To summarize there are thus 6 different
piece types, and each player is initially in
possession of 16 pieces:
1 King
1 Queen
2 Rooks
2 Knights
2 Bishops
8 Pawns
Each of these 6 piece types are identified
solely by the way they move. For instance,
the fact that the queen is stronger than the
rook is not because the queen as such has
higher rank than the rook (as in most card
games and board games such as Stratego).
Rather, the queen moves in a way superior
to the rook.
Objective of Chess
The objective of the game is to conquer the
opponent king. The king is thus the most
important piece in chess, although not the
strongest in terms of the ability to capture
opponent pieces. This actually is, as we shall
soon see, the queen.
The side to move is said to be in "check" if
his king is attacked by an opponent piece,
i.e. if the king could be captured
immediately by that piece if it was the
opponent's turn to move. It is illegal for the
side to move to leave his king in check or to
make a move that will allow the opponent to
capture his king immediately thereafter.
If the side to move is check and he has no
legal moves (i.e. no matter what he does, the
opponent can capture his king on the next
move), then he is said to be "check mate" or
just "mate" and has lost the game. The
objective of a chess game can now be stated
more precisely: To check mate the opponent
king.
Chess Move Notation
Various forms of chess notation exist for
describing the moves of a game. The most
commonly used form is the so-called
algebraic notation, where each square of the
board is identified by its "file" (column)
and "rank" (row). The files are described
from left to right by the letters 'a' to 'h',
whereas the ranks are numbered from 1 to
8 as shown on the diagram.
In the initial position, the white pieces thus
occupy ranks 1 and 2. For instance, the
white king is located at the square e1, the
black queen at d8, and the four central
squares are named d4, d5, e4 and e5.
The notation for a single chess move
basically consists of an indication of the
origin square followed by the destination
square. If the move is not a pawn move, the
origin square is prefixed with a piece letter
(K = King, Q = Queen, R = Rook, B = Bishop,
N = knight) indicating the moving piece.
When using figurine notation, the piece
letter is replaced by a miniature picture of
the moving piece.
For instance, the move Ng1-f3 indicates a
knight moving from the square g1 to f3,
whereas the move d2-d4 indicates a pawn
moving from d2 to d4. For capturing moves
the hyphen '-' is replaced with a 'x' (e.g.
Rc4xc8 for a rook on c4 capturing a piece on
c8). There are a few exceptions to these
rules which will be described later.
Two forms of algebraic notation exist: "long"
and "short" notation. In the long algebraic
notation (LAN) we indicate both the source
and destination square (e.g. Ng1-f3, Rc4xc8
and d2-d4). In the short algebraic notation
(SAN) the source square is omitted (e.g.
Nf3, Rxc8 and d4) unless this makes the
move ambiguous, i.e. if more than one piece
of the same type can move to the same
square.
For the time being we will stick with the
long notation because it is simpler although
somewhat bulky. We will return to the more
difficult but more compact and economic
short notation later. We suggest that you
select long notation from the "Notation"
submenu in the "Display" menu before
continuing.
2. Piece Movement
Now that the various piece types have been
introduced we are now in a position to
describe the rules governing the movement
of each piece. We shall start with the kings
followed by the rooks, bishops, queens,
knights and pawns. In each case we shall
illustrate the piece movement through brief
game samples.
NOTE: To see the legal moves for any piece
belonging to the side to move, you can hold
down the option key and click on the desired
piece. This will indicate all legal destination
squares for that piece with a blue frame. It
is recommended to use this facility often in
the following discussion.
The King
The diagram on the left shows a position
with a white king and rook versus a lonely
black king where White is to move.
White to move
As we will learn later, this is an easy win
for White, but for the moment let us forget
about the white rook and concentrate on the
kings.
A king can move 1 square in any of the 8
directions: up, down, left, right and
diagonally (hold down the option key and
click on the white king to see his moves).
Now, assume that white decides to move his
king right to the square e4 (select the "Redo
Move" command from the game menu):
1 Ke4 . . .
It is now Black's turn to move. Since his
king is on the edge of the board, he only has
5 available squares to go to.
As we will see later, the Black king can in
this piece configuration only be captured on
the edge of the board. To postpone his defeat
he therefore decides to move away from the
edge to the square g6.
1 . . . Kg6
It is now White's turn again, and we now
encounter an important exception to the
rule, that the king can move to any of the 8
squares surrounding him. It is namely
illegal for the white King to move to the
square f5, as this would enable the black
King to capture the white King immediately
afterwards. Thus there must always be at
least one square between the two kings.
2 Ke5 . . .
White instead moves his king to e5 to keep
the Black king from escaping too far from
the edge. Now it is Black's turn...
2 . . . Kf7
This concludes the movement of kings for the
moment. We will now introduce the rook.
The Rook
The rook can move both vertically and
horisontally but not diagonally. Contrary to
the King, the rook can move more than one
square at a time, but it cannot pass through
occupied squares (hold down the option key
and click on the white rook in the diagram to
see possible moves):
White to move
3 Rg1 . . .
This move cuts off the black king from going
to the g file. As before, it is illegal for a king
to expose himself to attack. If Black for
instance moved to g6, the White rook could
capture him by playing Rg1xg6.
3 . . . Ke7
4 Rg7+ . . .
This move directly threatens the Black king,
i.e. Black is in check which is indicated by a
"+" sign after the move.
Now Black is forced to the edge of the board,
since the white king controls d6, e6 and f6
and since the white rook controls f7 and d7
(and in fact the whole 7th rank).
4 . . . Ke8
5 Kd6 Kd8
6 Rg8#
Black has now lost the game since his king is
check mate (indicated by a "#" sign), i.e.
Black is check and he has no legal moves,
because no matter where his king goes,
White can capture him on his next move (of
course 5. ... Ke8-d8 is not Black's best
move. The move 5. ... Ke8-f8 still loses but
postpones the mate: 6. Rg7-e7 Kf8-g8 7.
Kd6-e6 Kg8-f8 8. Ke6-f6 Kf8-g8 9. Kf6-
g6 Kg8-f8 10. Re7-e6 Kf8-g8 11. Re6-
e8# mate).
The Bishop
The bishop is similar to the rook, the
difference being that bishops only move
diagonally (hold down the option key and
click on one of the bishops on the board to
see their moves). Note that the bishop on e3
cannot move to b6 or a7 in the diagram
because its path is blocked by the white
king:
White to move
A bishop thus always moves on identically
coloured squares, and is therefore weaker
than a rook that can control a whole file or
rank. A single bishop and a king also cannot
force mate no matter how the lonely king is
placed on the board.
Two bishops as in the diagram are sufficient
though to force mate (provided they are
moving on different coloured squares).
1 Bd4 . . .
This move illustrates the power of two
adjacent bishops. They are blocking the
right side of the board.
1 . . . Ke7
2 Bd5 . . .
Again "tightening" the grip by preventing
the black king from escaping.
2 . . . Kd7
3 Bf6 Kc7
4 Bc6 . . .
Now the black king is forced to retreat to the
edge of the board, which - as in the case of
the rook - is the only place where White can
force mate with two bishops.
4 . . . Kc8
5 Kb6 Kb8
6 Bd7 Ka8
7 Bg5 . . .
An important waiting move. The more
obvious move Bf6-e5 which takes away the
last free square from the black king actually
leads to a draw because of a special rule:
Although the black king has no legal moves
after Bf6-e5, he is not check mate because
he is not check. Instead black is said to be
"stale mate", which by definition is a draw.
7 . . . Kb8
8 Bf4+ Ka8
This is Black's only move, and now White
can force mate in the next move:
9 Bc6#
The Queen
The queen combines the movement of the
rook and bishop, and consequently makes the
queen stronger than both. Forcing mate with
the queen is a relatively simple task:
White to move
1 Qc7+ . . .
Forces the black king to the back rank.
1 . . . Kf8
2 Kf6 Kg8
3 Qg7#
Mate!
The Knight
The knight moves in a special manner,
which does not resemble that of the queen,
rook and bishop. The knight moves 1 square
in one direction followed by 2 squares
perpendicular to that direction. The knight
on d3 in the diagram can thus move to the
squares c1, e1, b2, f2, b4, f4, c5 and e5:
White to move
Hold down the option key and click on the
knight to see the moves.
Unlike the queen, rook and bishop the knight
can pass (or jump) over occupied squares.
A single knight cannot force mate no matter
how the lonely king is placed. It is possible
to check mate a lonely king with two
knights, but not if the lonely king "plays"
optimally.
1 Ne5+ Ke7
2 Nc6+ Kd7
3 Nxe8 Kxe8
The Pawn
The pawn is the weakest of all pieces. The
movement is defined by the following rules:
1) If the square immediately in front of the
pawn is empty, the pawn can move to that
square.
2) If the pawn is located on the second rank
(and hence has never been moved) it may
move two squares forward if both squares
are empty.
3) If the square left or right to the square in
front of the pawn is occupied by an enemy
piece, the pawn may capture that piece.
4) A pawn that advances to the 8th rank is
"promoted" to either a queen, rook, bishop
or knight. The choice is up to the player, but
normally a queen is chosen because it is the
strongest of the pieces. The notation for
promotion moves consists of appending an
"=" sign followed by a piece letter indicating
the selected piece (e.g. g7-g8=Q for a queen
promotion).
Thus a pawn can never move backwards but
only forward towards the opponent side of
the board.
White to move
The pawn on c2 can move to c3, but also to
c4 because it has not been moved before. The
pawns on b5 and f4 cannot move. They are
blocked by black pieces.
The pawn on h3 can only move to h4,
whereas the pawn on e5 can move to e6 as
well as capture the black pawn on d6.
The pawn on g7 can only move to g8 and
must be promoted to a queen, rook, knight or
bishop (hold down the option key and click
on the various white pawns):
1 g8=Q dxe5
2 fxe5 Kxe5
3. Special Rules
There are a few special rules in addition to
the already described movement rules:
1) Castling
2) En passant
3) Draw by repetition
4) The 50 move rule
5) Draw Offers
Castling
"Castling" is a special move that involves
both a king and a rook. In the diagram white
can castle "king sides" by moving his king to
g1 and the rook on h1 to e1. He also has the
option of castling "queen sides" by moving
his king to c1 and the rook on a1 to d1:
White to move
Note, that castling is considered a single
move even though it involves two pieces of
the same colour. The move notation for king
sides castling is "O-O" and for queen sides
castling it is "O-O-O".
Castling is only legal if the following
conditions are satisfied:
1) Neither the king nor the rook in question
may have moved before.
2) The squares between the king and rook
must be empty.
3) The king may not be in check.
4) The square to which the king moves may
not be attacked by the opponent.
5) The square between the king's current
and new location may not be attacked by the
opponent either.
In the diagram Black has lost his queen side
castling rights because the rook an a8 has
moved to c8. Even if he first plays Rc8-a8
he cannot castle queen sides (condition 1).
Black has not yet lost his king side castling
rights, but he is currently unable to
perform king side castling because the
square f8 is attacked by the White bishop on
b4 (condition 5).
Castling must always be performed by first
moving the king to either g1 or c1 (g8 or c8
for Black), and then moving the rook. In
Sigma Chess you only have to move the king;
the rook is moved automatically for you.
The castling move may seem a rather
strange move, but it was introduced to allow
the king to get into safety while at the same
time getting the rook into play. As such
castling is very useful and highly
recommended and occurs in almost every
game of chess.
En Passant
The "en passant" move is a special pawn
move where an opponent pawn is captured:
Black to move
The white pawn on c4 effectively blocks the
advance of the black pawn on d6. If Black
plays 1. ... d6-d5, White can capture the
black pawn by playing 2. c4xd5. There is
nothing strange about this.
The white pawn on g5 similarly blocks the
advance of the black pawn on f7, except that
here Black can play 1. ... f7-f5. This is
where the en passant rule can be applied,
allowing White to "capture" the pawn on f5
by playing 2. g5xf6EP. The black pawn is
said to have been captured "en passant"
(select "Redo Move" from the "Game"
menu):
1 . . . f5
2 gxf6EP
En passant is only legal immediately after an
opponent double move. If White had for
instance played 2. Kd3-e3 instead he would
lose the "right" to capture the black pawn on
f5 en passant.
The en passant rule may seem like a strange
move, but it was introduced in order to take
away some of the advantages of double pawn
moves, the reason being that it is somewhat
unfair that the white pawn on g5 cannot stop
the black pawn on f7.
Draw by Repetition
As we have seen previously, a game of chess
is drawn if there isn't sufficient material to
force mate (e.g. king and bishop versus
king, or simply king versus king). There
are other situations though where a game is
drawn even if one side is materially ahead as
in shown in the diagram:
Black to move
Things look very bad for Black, because his
bishop on f8 is subject to a devastating
attack by the White queen and rooks. Black
however saves the game as follows:
1 . . . Qe1+!
2 Kh2 . . .
Apparently Black hasn't achieved anything.
His bishop is still subject to capture and he
obviously cannot checkmate White.
2 . . . Qh4+
Again, White only has one move:
3 Kg1 . . .
It may now be tempting to capture the knight
on c4. But this obviously loses after 4.
Rc8xf8#. Instead Black plays:
3 . . . Qe1+!
And now we are back at the position after
Black's first move, and there is nothing
White can do about this.
4 Kh2 Qh4+
5 Kg1 Qe1+
Black can continue like this as long as he
likes, giving checks on e1 and h4. So despite
his great material advantage, White in fact
never gets the opportunity to capture on f8.
The game is therefore a draw.
By definition a game is a "draw by
repetition" if the current position has
occurred three times with the same player
to move (not necessarily three times in a
row):
6 Kh2
Draw by repetition, since this position has
occurred two times previously after White's
2nd and 4th move. A draw by repetition can
also occur in materially even positions,
where neither side can make any progress.
The 50 Move Rule
The 50 move rule states that a game is
drawn if no pieces have been captured and no
pawns have been moved in the last 50
moves.
White to move
In the diagram, White cannot win unless
Black makes a mistake, despite White's
material advantage. If it wasn't for the 50
move rule, White could play on almost
endlessly (only bounded by the "Draw by
repetition" rule which is, however, not
very useful in this situation) hoping for
Black to make a mistake.
Draw Offers
A game is also drawn if both players agree
on this. More precisely, a player can offer a
draw immediately after performing his
move. If the opponent accepts the draw offer,
the game is considered drawn. The opponent
must either accept or decline the draw offer
before performing his move.
Note that a draw offer is actually considered
part of the move after which the offer is
issued. In a real over the board game with a
human opponent, the draw offered should
therefore be issued immediately after
performing a move but before pressing the
chess clock (Sigma Chess doesn't care about
this; you can offer a draw at any time after
your move when the program is thinking).
4. A Sample Game
We conclude this tutorial with a sample
game where the various chess rules will be
illustrated. The purpose here is not to play a
strategically correct game.
1 d4 . . .
It is generally a good idea to gain control
over the centre in the start of a game by
playing d2-d4 or e2-e4. This also has the
advantage of opening up for the bishops; in
this case Bc1.
1 . . . d5
2 Nf3 . . .
White moves his knight out to enable
castling as soon as possible.
2 . . . Nc6
3 e3 . . .
Opens up for the bishop on f1.
3 . . . Nf6
4 Bb5 . . .
Pins the knight on c6, which is now unable
to move. By doing so the black king would be
in check, and according to the rules it is
illegal for a player to expose his king to
check.
4 . . . g6
5 O-O . . .
White castles and brings his king into
safety.
5 . . . Bd7
Unpins the knight on c6, since it can now
move without exposing the black king to
check.
6 c4 dxc4
7 Bxc4 Bg7
8 d5 . . .
Threatens to capture Nc6, which should
therefore move eventhough Black could
recapture. This is because the knight is
stronger than a pawn.
8 . . . Nb8
9 Nc3 c5
Now the pawn on d5 can capture en passant:
10 dxc6EP Bxc6
11 Qxd8+ . . .
Black is now in check and only has one legal
move:
11 . . . Kxd8
All other moves are illegal since the king is
left in check.
12 Rd1+ . . .
Again Black is in check but here he has other
options than moving the king. He can for
instance also play 12. ... Nb8-d7 or 12. ...
Bc6-d7.
12 . . . Ke8
13 Nd4 . . .
Note that Black has lost his castling rights
because his king has already moved. In
particular, Black cannot castle with the
rook on h8 even though the squares f8 and
g8 are both unoccupied.
13 . . . e6
14 Nxc6 Nxc6
15 Bb5 Ke7
16 Bxc6 bxc6
17 e4 Rhd8
18 Bg5 Rxd1+
White is check and must capture the black
rook on d1.
19 Rxd1 e5
20 Bxf6+ Bxf6
21 f3 Rd8
22 Rxd8 Kxd8
In the resulting endgame the goal for each
player is now to promote a pawn.
23 Kf2 Be7
24 Ke3 f5
25 exf5 gxf5
26 g4 fxg4
27 fxg4 Kd7
28 Ke4 Bb4
29 a3 Bxc3
30 bxc3 Ke6
Black must defend e5.
31 h4 a5
32 c4 h6
33 g5 hxg5
34 hxg5 c5
35 g6 Kf6
36 g7 . . .
White sacrifices this pawn. Black has to
capture and then White can take e5 and c5.
36 . . . Kxg7
37 Kxe5 Kf7
38 Kd5 Ke7
39 Kxc5 . . .
Black is lost now.
39 . . . Kd7
40 Kb6 Kd6
41 c5+ . . .
Now this pawn will soon promote.
41 . . . Kd7
42 Kb7 Kd8
43 c6 a4
44 c7+ Ke7
45 c8=Q Kf6
46 Qc6+ Ke7
47 Qxa4 Kf6
48 Qe4 Kf7
49 a4 Kf6
50 a5 Kf7
51 a6 Kf6
52 a7 Kf7
53 a8=Q . . .
It is possible to have more than one queen.
53 . . . Kf6
54 Qf8+ Kg5
55 Qef4+ Kg6
56 Q4f5#
Checkmate.
This sample game concludes this tutorial of
the rules of chess.