Reversi

Othello Strategy and Openings ― How to Win at Reversi

The secret to winning at Othello is not capturing more discs, but cutting down the moves your opponent can make (restricting their mobility). The game is decided only when the last move has been played: you can be far behind in discs along the way and still win if you have more at the end. The first half of this guide covers the ideas that make a beginner stronger fastest, in order of impact. The second half explains the standard openings with diagrams and move sequences.

Golden rule ①: a corner disc can never be flipped

A disc in one of the four corners can never be outflanked, so it can never be flipped again (a stable disc). Once you hold a corner, the discs along the edges running from it become stable too. Take corners and don't give them away — this is the single most important point in Othello strategy.

Golden rule ②: avoid X-squares and C-squares

• X-squares are the squares diagonally next to a corner (b2, g2, b7, g7). Playing there is the classic way to hand your opponent a corner, and the shape that costs beginners the most.
• C-squares are the edge squares next to a corner (a2, b1 and so on). They also tend to open the way to a corner, so handle them with care.

Turn it around: make your opponent play an X- or C-square and the corner is yours. That is also what you aim for when attacking. But a beginner who follows only this rule can be broken down by a player who offers a corner as bait (see the beginner trap).

Golden rule ③: flip few discs in the opening

If you flip lots of discs early, your discs spread to the outside (frontier discs), and your opponent gets more moves while you get fewer. Through the opening and midgame, flip as few as you can and squeeze your opponent until they have no move and must pass. The disc count swings back all at once in the endgame.

Technique ①: choose the move with the lowest openness

In Japan, the number of empty squares around the discs you flip is called kaihōdo, or openness. The lower the openness of a move, the fewer new moves it gives your opponent. When several moves look about equal, pick the one that flips discs on the side already surrounded by discs. Many moves in the standard openings are exactly the lowest-openness move in that position.

Technique ②: quiet moves

A quiet move flips only inner discs that are already surrounded (Japanese players call the typical case nakawari, "splitting the middle"). Because it puts no discs on the outside, it keeps openness low. Remember: "flips few discs and doesn't spread outward" = a good move.

Technique ③: use parity to get the last move in the endgame

In the endgame, if you leave each empty region to your opponent with an even number of squares, you get the last move in that region. Discs flipped by the last move in a region can't be flipped back, so they count straight toward your score.

What openings are ― start with the three families

An opening is a sequence of early moves considered best for both sides. Wherever Black plays the first move, rotating the board gives the same position, so game records write the first move as f5 (columns a–h from left to right, rows 1–8 from top to bottom). Some English opening lists, such as Robert Gatliff's, start from c4 instead; rotate the board 180 degrees and it is the same position. In the diagrams below, the number on a square shows which move was played there. Each diagram plays automatically from its example position, and the buttons below it pause, step forward or step back one move.

Openings split into three families by White's second move. Against Black's f5, the vertical reply d6 is the Perpendicular Opening, the diagonal f6 is the Diagonal Opening, and f4, side by side, is the Parallel Opening. The Perpendicular is the most common in real games, followed by the Diagonal. The Parallel is rarely played, because White struggles once Black answers correctly.

On Black's third move, the Perpendicular splits into the Rabbit (c5) and the Tiger (c3). The Diagonal almost always goes to e6 and into the Cow family, and the Parallel goes to e3 and the Mouse. In Japan, the Rabbit, Tiger, Cow and Mouse have long been called the four great openings — the four basics.

Rabbit and Rose ― a straight road to learn first

Against the Perpendicular, Black's third move on c5 is the Rabbit. c5 flips just one white disc, d5 — a quiet move, and one of the lowest-openness choices for move 3. Move 5, e3, is also the lowest-openness move in its position.

The Rabbit has few branches and leads to the Rose, which runs almost as a single line up to move 10. It comes up often whether you play Black or White, so it is a good first opening to learn. It is named after Brian Rose, the American player who was World Othello Champion in 2001.

After the Rose, move 11 branches into lines such as the Rose-Birth, which attacks on the diagonal with g3 (called "Sharp Rose" in Japan), and the Flat Rose with g4. First, play through the 10 moves again and again until your hands remember them.

Tiger and Rose-Bill ― the serious choice of strong players

Against the Perpendicular, Black's third move on c3 is the Tiger. The basic shape is White d3 on move 4, Black c4 on move 5 and White f4 on move 6. Move 5, c4, is the lowest-openness move in its position.

The Tiger has a great many variations depending on move 7, and it is used a lot in strong players' games. To start, aim for the Rose-Bill, which goes from c5 on move 7 (the Many Blacks line) to c2 on move 9. That makes it easier to remember. In Japan the Rose-Bill is called hanagata, "the flower shape".

Cow, Heath and Buffalo ― the Diagonal Opening

Against the Diagonal, Black's third move is almost always e6. It flips only White's e5, and its openness is far lower than any other choice. After move 4 on f4, the lines split on Black's fifth move.

Move 5 on e3 is the Cow, the basic Diagonal line and the one played most often. Move 5 on g5 gives the Heath (also known by its Japanese name, Tobidashi), and c3 gives the Buffalo. The Cow and the Heath, along with the Tiger, are often recommended as the first openings for beginners.

Playing move 5 on g7 instead gives the X-square Opening (in Japan, bōsō-ushi, "the runaway cow"). It is an X-square move next to a corner and normally leaves White well ahead, but against a beginner who wants corners it becomes a trap. The next section explains how.

A beginner trap ― bait a corner and catch players who only "avoid the squares next to corners"

New players follow two rules: "take corners" and "don't play next to a corner (X- and C-squares)". Both are good advice, but an opponent who thinks of nothing else can be caught by using a corner as bait.

The bait is the X-square Opening. When Black deliberately plays g7 on move 5, White gets the chance to take the h8 corner.

A White player who wants corners jumps on h8 right away. From then on, Black removes, one by one, the squares White can play other than those next to corners. The diagram below is one example from the X-square Opening to the end of the game.

• Move 6: White grabs the h8 corner
• Moves 7–23: Black removes White's moves. After move 23 Black has only 6 discs and White 21, yet White's only moves are four squares next to corners
• Moves 24–33: White is forced onto b1, g1, g2 and h2, all next to corners, and Black takes the a1 and h1 corners
• Move 34 onward: White passes almost every turn. In the end White is left with a single disc, on h8

The trick is to count, every move, how many moves White has that aren't next to a corner. Even if you are behind in discs, once that number reaches zero White has to play next to a corner.

Against an opponent who doesn't jump at the corner, though, the X-square Opening is a big loss. If White leaves h8 alone and answers with a quiet move, the trap fails. And when you are White yourself, don't just avoid the squares next to corners — also check whether your own mobility (the number of moves you have) is shrinking.

The Parallel Opening and the Mouse ― a shape where White tends to lose ground

Against the Parallel, Black's third move e3 is the only good move (the lowest-openness choice). White f6 and Black d3 then give the Mouse. It tends to favor Black, and White would rather avoid it. If your opponent plays the Parallel, punish it with the Mouse.

Opening list

All the openings covered above, in one table. Each name links to its diagram.

How to learn openings

• Start with just three: the Rabbit, Tiger and Cow. Learning them to move 5 or 6 is enough. If you extend the Rabbit to move 10 of the Rose, you can use it as Black or as White.
• Learn each move together with its reason. A move whose reason you can see — "low openness", "a quiet move" — comes back to you without rote memorization.
• When your opponent leaves the book, go back to the golden rules and techniques: pick the move that flips few discs and puts none on the outside.
• At some stages, playing lots of games makes you stronger faster than studying openings. Move on to openings once you have a feel for corners and X-squares, and they will sink in faster.

Practicing against the computer to get stronger

Start on "Easy" to "Normal" to get the feel for taking corners and never playing X-squares. Once you are comfortable, move up to "Hard" or above and practice play that cuts down your opponent's mobility. After learning some openings, try playing only the opening by the book against the computer and thinking for yourself from there. Playing both Black (first) and White (second) quickly deepens your understanding of opening shapes.