# What are Key Squares or Critical Squares?

What is your best definition of Key Squares in King and Pawn vs King Endgame Theory? Please provide graphics if possible. Is there a difference between "Key Squares" and "Critical Squares" or are these terms interchangeable?

• This site says they are the same. en.wikipedia.org/wiki/Key_square – Tony Ennis Jul 12 '12 at 14:51
• Thanks, Tony. I was actually aware of the wikipedia answer. I thought that a detailed post on the topic might be good here on Chess SE. Would you mind writing up an answer to both parts? Or maybe my question should be closed as to easily "Googlable"? My meta post: meta.chess.stackexchange.com/questions/144/… – Robert Kaucher Jul 12 '12 at 15:34
• I have nothing substantive to add so I should not answer. I googled because I didn't know the answer, and found what seems to be something definitive. – Tony Ennis Jul 12 '12 at 16:21
• If "key square" and "critical square" are just different names for the same concept (which seems to be the case), then there's not much of an answer to give to that part of the question. It then seems that the real meat of the question here is, "what is a key square?" The current text and title rather downplay that, and instead highlight the key/critical distinction. So if it's right that that's not really the interesting part, perhaps the question should be edited to highlight the other (e.g. a title of "What is a key square?" instead of "Key Squares and Critical Squares"). – ETD Jul 12 '12 at 16:22
• Edits have been made as suggested, Ed! – Robert Kaucher Jul 12 '12 at 17:12

The terms Key Squares and Critical Squares are sometimes used interchangeably in chess literature on `King vs. King and Pawn` endgames.

A square is called a Key Square when occupation of it by the attacking king will secure a win regardless of which side is to move.

## 2nd through 4th Ranks

In this example image the Key Squares for the white pawn are `e6`, `f6`, and `g6`.

``````fen=8/8/8/8/5P2/8/8/8/
``````

## A Pawn that Crosses the 5th Rank has More Key Squares

In this image the pawn on `f5` has two sets of key squares: `e6`, `f6`, and `g6` as well as `e7`, `f7`, and `g7`. If White's king can occupy any of those 6 squares he can secure the win.

``````fen=8/8/8/5P2/8/8/8/8/
``````

## The Rooks Pawn are Exceptions

These positions show a draw regardless of which side has the move.

`fen=5k1K/8/7P/8/8/8/8/8/ and fen=7k/8/7K/7P/8/8/8/8/`

In the first position Black can simply shuffle his king between `f7` and `f8` and White makes no progress. In the second image `1. Kg6 Kg8` `2. h6 Kh8` `3. h7` stalemate 1/2 - 1/2 and `1... Kg8` `2. Kg6 Kh8` `3. h6 Kg8` `4. h7+ Kh8` with stalemate or loss of the pawn 1/2 - 1/2

## Resources

Wikipedia on Key Squares

Endgame Simulations (against a computer)

ChessDiary #2 - Monday Endgame Pawn Endgame - Key Squares

• Definitely a great answer to the question topic. With added images, anyone would be understanding the definition of a key square in no time! Does anyone mind doing a video in the efforts to benefit the further enhancement of our understanding of key squares? A simple chess game consisting of a few moves by the white and subsequent counter moves by the black or vice versa would suffice. Or perhaps more examples in the form of more images and supporting explanation that is detailed like the above with exact square locations "E7", "F6" etc. Would appreciate the kind help and looking forward to an – JamesBennett Nov 2 '12 at 8:58
• @JamesBennett, welcome to the site! I converted the post you originally made into the comment above, since it was clearly intended to be a comment on Robert's answer. Once you have 50 reputation, you'll be able to freely comment on other people's posts directly: chess.stackexchange.com/privileges – ETD Nov 2 '12 at 12:35
• Actually there is a lot more to key squares than those squares, those are for king + pawn vs king and similar positions. – user707 Nov 4 '12 at 14:41
• Which is what the question pertains to. – Robert Kaucher Nov 5 '12 at 1:03

I'm reading Fundamental Chess Endings by Karsten Muller and Frank Lamprecht right now, and the authors seem to imply there is a distinction between key squares and critical squares. On page 14, there is a list of symbols used in the text. A circle is used for a critical square and a star is used for a key square. So, there is an implied difference in this book. But I am puzzled as to what the difference is. "Key square" is defined on page 21 but "Critical square" is not defined before the authors start casually using the term. To add to the confusion, the authors use the circle symbol in diagrams on page 24 but refer to the squares marked with a circle as key squares.

Also, the terms key squares and critical squares are used in more endings than just king and pawn vs. king.