Blocked Paths

Part of the Fundamentals section of Coddy's Chess journey. Lesson 9 of 41.

Rook, bishop and queen share one law that every diagram so far has quietly ignored: a sliding piece cannot pass through another piece. Its line of movement stops at the first piece it meets. Watch what one pawn does to a rook:

White rook on a1 blocked on the a-file by a white pawn on a4

White's own pawn on a4 cuts the file. The rook may go to a2 or a3, but a4 and everything beyond it are off limits.

When the blocker is a friendly piece, that is the whole story: you can never land on your own piece, so the rook stops one square short. When the blocker belongs to the enemy, you get a better option:

White rook on a1 can capture a black pawn on a4 but not pass it

Now the pawn on a4 is Black's. The rook may slide up and capture it, but the squares behind it are still out of reach.

Capturing means the rook stops on the pawn's square and the pawn leaves the board. Passing through is never allowed, friend or enemy. The same law rules the bishop and the queen, and it explains something you can check against chapter 1's starting position:

White bishop on c1 with both diagonals blocked by white pawns on b2 and d2

This bishop has no legal moves at all: its own pawns on b2 and d2 block both diagonals.

That is exactly the bishop's situation on move one of every game. Until a pawn steps aside, the sliding pieces are asleep behind the pawn wall, which is why real games open with pawns and knights.

Try it yourself

White's rook stands on a1 and White's own pawn on a4. Click any square the rook can legally move to.