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This page is written by the game's inventor, JT K.

Share Squares

Chess involves a fight for space and material, and this particular variant adds an extra element of complexity to both – particularly in the opening. It can be played on a standard board and pieces, although one could likely add this general concept to other variants.


(Same setup as standard chess, but players can place the shared pieces outside the board near the corner squares (as discussed in the Notes section).)


In this article, the word "piece" includes pawns. This variant has the same piece movement and game objective as standard chess, but the center four squares (d4, d5, e4, e5) are known as "share squares." Each of these four squares can hold up to 2 pieces (2 black, 2 white, or 1 black and 1 white piece).


"Inactive square" - a share square with only one piece on it (either black or white) That piece cannot be captured, nor can it capture directly. It may move normally off of that shared square, unless the movement would capture a piece. This means that no piece on an inactive square is delivering check (although moving it onto a regular square from there might legally deliver check or checkmate). Sliding pieces such as bishops, rooks and queens can move "through" inactive squares as if they are empty squares. If any piece (enemy or friendly) moves onto that share square (as the 2nd piece to move onto it), see the following rule:

"Active square" - a share square with two pieces on it. Either piece may capture from that square or can be captured on that square. In other words, there is no room for a third piece (hence the alternate title of this variant, "Three's a Crowd.")

Here are the three types of active squares:

"Double black square" - a share square with two black pieces on it.

"Double white square" - a share square with two white pieces on it.

"Gray square" - a share square with 1 black and 1 white piece on it.

If a player moves onto his/her opponent's double square, then said player who does the capturing decides which of the two pieces is captured. The double square would then become a gray square, and either of those pieces can still be captured or capture from there (unless someone moves a piece off it – then it would become an inactive square).

Kings may move into the shared squares and usually behave just as other pieces, but these additional 2 rules apply to avoid stalemate:


When playing this game on a physical chess set, you can use pieces that are much smaller than the squares in order to fit two pieces in the share squares. However, this author would recommend the following method: When a piece is moved onto an empty center square, it can be first placed outside the chess board, near the corner that corresponds to the center square corner it inhabits (near a1 for the d4 square, near h8 for the e5 square, etc.) - - The 2nd piece on the share square would be placed on that square itself. This method would let both players know that if a piece is actually on the center square, it is "active" and if there is only the outside piece seen, it is still inactive (1 piece on it)

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By JT K.
Web page created: 2017-04-23. Web page last updated: 2017-04-23