Lesson 6 of 62 min read
Three moves that do not follow the rules you have just learned. Every one of them is legal.
The king moves two squares towards the rook, and the rook jumps over him and lands on the far side. Both pieces move on the same turn, which happens nowhere else in chess. It is the standard way to get the king out of the middle of the board.
You can only castle if neither of those two pieces has moved yet and the squares between them are empty.
The same move in the other direction. The king goes two squares towards the rook on the a-file, and that rook hops over to d1. The king ends up one square further out than he does kingside, and there is one more square to clear first.
You also cannot castle out of check, or through a square an enemy piece is attacking. A king may never cross a square he could be taken on.
Get a pawn all the way to the far end of the board and it turns into any piece you choose. You are not limited to pieces you have already lost: two queens on the board at once is perfectly legal.
Nearly everyone takes the queen, and nearly everyone is right to. Once in a while a knight is better, because a knight can do the one thing a queen cannot: give check from an L-shape.
The strangest rule in chess, and the rarest. If a pawn uses its two-square first move to slip straight past an enemy pawn, that enemy pawn may capture it anyway, landing on the square it skipped over. It is the one capture that does not finish on the captured piece's square.
You have to take immediately. Play anything else and the chance is gone for good.
Six lessons in, you know every rule there is. Everything from here is practice, and the fastest practice there is comes from puzzles: real positions, one good move to find.