Every Illegal Move in Chess – A Complete Guide

This is the complete list of illegal chess moves:

1. Moving a Piece off the Board
2. Moving a Piece Beyond Its Allowed Range
3. Capturing Your Own Pieces
4. Moving a Nonexistent Piece
5. Moving a Piece Through Occupied Squares
6. Putting Your Own King in Check
7. Ignoring a Check
8. Invalid Castling
9. Invalid En Passant
10. Invalid Promotion

I encourage you to read on to fully understand each case.

If you’re new to the game of chess, the concept of illegal moves is one you may find a bit troubling.

Just how many illegal moves are there?

In this comprehensive guide, I lay down each and every single illegal chess move — no matter how trivial it may seem.

1. Moving a Piece off the Board

Let’s start things off with the most basic illegal move.

You cannot move a piece to a square off the chessboard.

You have 64 squares to play on. Stay on them.

2. Moving a Piece Beyond Its Allowed Range

You cannot make a move that doesn’t adhere to a piece’s allowed range of movement.

Here’s a quick refresher of how every piece moves:

  • King: Moves only one square in any direction.
  • Queen: Moves any number of squares horizontally, vertically, or diagonally.
  • Rook: Moves horizontally or vertically any number of squares.
  • Bishop: Moves diagonally any number of squares.
  • Knight: Moves in an L-shape: two squares in one direction and then one square in a direction perpendicular to the first move. It’s the only piece that can jump.
  • Pawn: Moves forward one square but captures diagonally. On its first move, a pawn can choose to move forward two squares.

So, for example, it’s illegal to move a knight diagonally.

Here’s an illustration of all the squares a knight has access to:

The knight can only move to the green squares.
The knight can only move to the green squares.

3. Capturing Your Own Pieces

You cannot move a piece to a square occupied by a piece of the same color.

In other words, friendly fire is not allowed.

Obvious, right?

4. Moving a Nonexistent Piece

You cannot make a move with a piece that is not part of the game.

In other words, once a piece has been captured, you can’t just bring it back.

A very trivial one, but it perhaps may be worth mentioning for complete novices.

5. Moving a Piece Through Occupied Squares

You cannot move a piece through squares occupied by other pieces.

We previously saw in Rule #3 that a piece cannot land on a square taken by a friendly piece, but here, we’re saying that no piece can pass through occupied squares — whether the squares are occupied by your pieces or your opponent’s.

Since the knight is the only piece that can jump, it’s the only exception to this rule.

For example, in the following illustration, the bishop is trapped. It cannot move anywhere as all the diagonals are blocked by pawns.

This bishop is trapped as it's blocked by its own pawns.
This bishop cannot move anywhere as it’s blocked by its own pawns.
A knight can jump over pieces.
A knight can jump over pieces.

6. Putting Your Own King in Check

You cannot make a move that puts your king under attack.

The simplest example would be moving your king to a square that is controlled by an enemy piece.

In this position, the White king cannot move forward as the Black king controls all three squares.
In this position, the White king cannot move forward as the Black king controls all three squares.

However, the piece being moved doesn’t necessarily have to be the king itself.

Sometimes, moving a different piece can reveal an attack on your king. Such a move is not allowed.

Here’s an example.

White cannot move the highlighted pawn as this would reveal the bishop's attack on the king.
White cannot move the highlighted pawn as this would reveal the bishop’s attack on the king.

7. Ignoring a Check

You cannot ignore an attack on your king. You must respond to it.

If your king is in check, you are forced to deal with it in one of three ways:

  1. Capture the checking piece.
  2. Block the check with a piece, defending your king.
  3. Move your king out of check.

Any other move would be illegal.

8. Invalid Castling

You cannot castle under conditions that violate the rules.

Castling is a two-in-one move which allows the king to move two squares towards a rook on its home square, while the rook moves one square across from the king. It is used to keep the king safe and protected.

However, it is governed by specific rules that must be followed. Here’a short video by Chess.com summarizing these rules:

9. Invalid En Passant

You cannot play en passant under incorrect conditions.

The en passant rule allows a pawn to capture an opponent’s pawn when it advances two squares as if it had only moved one square forward.

The option to play en passant is only available on the very next move after your opponent advances their pawn two squares. It’s a one-time opportunity, take it or leave it.

Also, en passant only applies to pawns; it does not work for other pieces.

10. Invalid Promotion

You cannot promote to a piece other than queen, rook, bishop, or knight.

This should be obvious, but some people wonder whether they can promote to a king, or even not promote at all and keep their pawn.

The answer is no. Any pawn that reaches the back rank must promote, and it can only promote to a queen, rook, bishop, or knight.

If you’re wondering why a pawn cannot promote to a king, check out my answer to this question on Quora.

There you have it. These are all the illegal moves in chess.

If you have any questions or insights you’d like to share, please go ahead and leave me a comment. I’d love to have a chat with you.


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