Reversi Edge Play and Midgame Solid Formations

When playing Reversi against a smartphone AI, have you ever felt your position suddenly fall apart in the midgame? Even after an even opening phase, rushing to grab edge discs often lets your opponent take control—a common trap even for intermediate players. In this article, we review the basics of Reversi edge play and explain practical concepts to stay solid through the midgame.

Edge Square Names and Squares to Avoid First

This diagram shows a midgame board where White has lined up 4 discs from c1 to f1 along the top edge. At both ends of the edge, b1 and g1 are C-squares, and diagonally adjacent inside are the X-squares b2 and g2. When considering edge play, start by telling these 2 types of squares apart.

The squares along an edge run in order from corner to corner: C-square, A-square, B-square, B-square, A-square, C-square. The most dangerous spot is not on the edge itself, but the X-square diagonally adjacent to a corner (such as b2); playing here during the opening phase or midgame makes it very easy to surrender a corner. The next square to treat with caution is the C-square right next to a corner. Discs placed in a corner can never be flipped until the game ends, so avoiding openings that give away corners forms the very foundation of edge play. Memorizing these names lets you review transcripts and read commentaries with clear terms for where danger lies.

Strong AI opponents will never miss a chance to seize a corner if you play into a C-square or X-square carelessly. Before making a move on an edge, build the habit of checking move by move whether your opponent has a line to take a corner.

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The fastest way to master these concepts is to test them in real play. With an AI that computes entirely on-device, you can finish full games even with no internet connection.

Contesting Edges by Waiting Rather Than Entering C-Squares

This diagram shows the board right after Black played into the C-square at g1 from the previous position. While playing g1 allows Black to outflank and flip White's f2, White can play the corner at h1 to outflank and flip Black's g1 right back. This is a classic pattern where trying to extend discs along an edge ends up giving away a corner.

When fighting over an edge, waiting for your opponent to run out of viable moves on that edge is often far more advantageous than diving into a C-square yourself. Edge discs can always be flipped back until they link to a corner, so checking the relation between both C-squares and the corners is far more vital than counting how many discs you line up. The core principles of edge play are:

• Only play a C-square after confirming that the disc formation prevents your opponent from taking the corner.
• Once discs line up on an edge, check the relation between both C-squares and the corners first.
• Avoid rushing to fill the edge, preserving edge moves exclusively for yourself.

In the smartphone Reversi app Patent War, you can rewind transcripts after matches to review free AI commentary. Looking back to see which move entered a C-square and gave up a corner will naturally sharpen your edge play.

Handling Remaining Edge Empty Squares in the Endgame

When empty squares remain along an edge in the endgame, the first thing to check is still their relationship to the corners. If an empty square is a C-square, check whether playing there gives away the adjacent corner before making your move. For details on deciding move order by counting empty squares, see our article on parity.

Edge discs only become hard to flip once they are connected to a corner. In the endgame, deciding who captures the corner carries far more weight toward your final disc count than merely grabbing a few extra edge discs.

Because the AI match mode in Patent War works offline, you can play matches during spare moments like commutes and get a feel for waiting patiently rather than forcing edge moves.

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Patent War is a Reversi app set in a steampunk world. Start AI matches and journeys for free.