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Official Reversi Rules and Gameplay Explained

Reversi—also popularly known as Othello—is governed by a set of clear and elegant rules that produce remarkably deep strategic play. Although the mechanics are simple, understanding the official rules precisely is essential for consistent improvement and competitive-level strategy.

This guide explains every core rule of Reversi in detail, including legal moves, flipping mechanics, passing, corner behavior, stability concepts, and endgame conditions. Examples throughout the article help clarify subtle points that beginners often misunderstand.

These rules follow the standard modern Reversi conventions used in online and tournament play, including PlayFaceToFace.com.

Game Equipment and Starting Position

Reversi uses an 8×8 board and 64 discs, each with a black and white side.

Starting Layout

The game starts with four discs in the center arranged diagonally: D4 (White), E5 (White), D5 (Black), and E4 (Black). This symmetrical arrangement ensures fairness: both players begin with the same positional potential.

Who Moves First?

Black always moves first. This convention is universal across competitive and digital versions of Reversi.

Legal Moves: What Counts as a Valid Play

A move is legal only if it flips at least one of the opponent's discs.

To be legal:

The square must be empty.
The disc placed must flank one or more continuous lines of opponent discs.
That line must end with a disc of the current player's color.

Only moves that satisfy all conditions are allowed.

Legal Lines

Flips may occur in eight directions: horizontal (left, right), vertical (up, down), and diagonal (four diagonals).

At Least One Flip Required

If a placed disc flips zero opponent discs, the move is illegal and the player must choose another square. Beginners often misjudge diagonal lines; careful scanning is required.

Flipping Mechanics Explained

Flipping is the signature mechanic of Reversi. When you place a disc, all flanked lines become your color, flips occur immediately, and multiple directions may flip simultaneously.

What Counts as a Line?

A valid line contains one or more opponent discs, ends with your disc, and has no empty squares between the placed disc and the endpoint.

Can You Flip in Multiple Directions?

Yes. One move may flip one line, several lines, or entire rows or diagonals. This produces the dramatic board swings characteristic of Reversi.

Passing Rules

If a player cannot make any legal move, they must pass. Passing is mandatory, not optional. The opponent then takes their turn. If both players have no legal moves, the game ends. Passing becomes important in advanced play because mobility decides midgame advantage.

Game End Conditions

A Reversi game ends when no legal moves remain for both players, or all 64 squares are filled.

At the end of the game:

Count all discs showing each player's color
The player with the majority wins

There are no incremental scoring systems—final board count is everything.

Examples of Legal and Illegal Moves

These examples help clarify confusing rule interactions.

Example of a Legal Horizontal Flip

Board line: White — White — Black. If Black places to extend this line so it becomes: Black — White — White — Black, then the two Whites between Black discs flip to Black.

Illegal Move Example: No Flanking Disc

If Black places a disc that does not trap opponent discs between two Black discs, the move is invalid. A move must create at least one continuous flanked line.

Diagonal Flip Example

White at C3, Black at D4, White at E5. If White plays at B2, then B2 → E5 creates a diagonal line and C3 and D4 flip to White. Diagonal flips are often overlooked by beginners.

Core Strategic Rule Concepts Beginners Often Miss

While not rules in the strict sense, these principles arise directly from how the rules interact and are essential to understanding the game properly.

Corner Stability Rule

Corners (A1, A8, H1, H8) are crucial because they cannot be flipped once taken, they often stabilize entire regions, and they provide strategic leverage. The rule-based behavior of corners makes them the most valuable squares on the board.

Edge Behavior Rule

Edges behave differently from interior squares: they have fewer adjacent flanking possibilities, they are less volatile, and they affect mobility significantly. Edges become powerful in the mid-to-late game.

X-Square Danger Rule

Squares diagonal to corners (e.g., B2, G2, B7, G7) are extremely risky early because playing there often gives the opponent the corner, and flipping opportunities around X-squares are predictable and exploitable. The rules create this vulnerability because X-square moves enable the opponent to flank toward the corner.

Forced Move Principles in Reversi

Reversi does not require forced captures like Checkers, but it enforces legal move availability. This leads to advanced strategic consequences.

Having More Mobility Is Always Better

If your opponent has no moves, you gain an extra turn, they may be forced to pass, and you can force corner or edge control. Mobility dominates strong Reversi play.

Controlling When Your Opponent Passes

In advanced endgame play, you may intentionally reduce your moves to force a pass, increase theirs to control timing, or manipulate parity (odd/even region filling). This is central to expert Reversi strategy.

Stability Rules and Final Disc Behavior

A disc that can never again be flipped is called a stable disc. Stability arises from corners, edges connected to corners, full rows or columns controlled end-to-end, and endgame fill behavior. Stable discs decide the final score.

Reversi Rule Clarifications That Beginners Often Misunderstand

You Must Flip at Least One Disc

Even if a move seems strategically good, it is illegal if it flips nothing.

You Cannot Jump Over Empty Squares

Flanking must be continuous, without gaps.

Diagonals Must Be Straight

Only true diagonal lines count—no curved or broken patterns.

Passing Is Only Allowed When No Move Exists

A player cannot choose to pass voluntarily.

Disc Colors Matter Only at Game End

Midgame disc count does not indicate who is winning.

You Cannot Skip a Flip

All valid flips in all valid directions are mandatory.

Example: A Full Turn Breakdown

Imagine White plays F5. If the placement flanks opponent discs horizontally at E5, vertically at F4, and diagonally at E6 and G4, then all four directions flip simultaneously. This illustrates why moves that flip many discs at once may backfire—they often give the opponent more mobility.

Summary of Official Reversi Rules

Category	Official Rule
Move Legality	Must flip at least one opponent disc
Directions	Horizontal, vertical, and diagonal
Turn Order	Black goes first, alternate turns
Passing	Allowed only when no legal move exists
End Condition	Both players stuck OR board is full
Scoring	Majority of discs at end wins
Flipping	All valid lines flip immediately
Stability	Corners and connected discs cannot be flipped

These rules form the foundation for all Reversi strategy, from beginner-level play to expert-level calculations.

Ready to Play?

Now that you understand the official rules of Reversi, jump in and start playing with real opponents online. Apply these rules with precision and develop your strategy.