Okay, hi, I'm David Sullivan from Chess NYC. Today, I wanna talk about pawns and pawn promotion. At the beginning of a game of chess, we have to bring out our pawns in order to free our pieces, but at the end of the game, we want to promote our pawns so that we can have extra material. Let's say we reached a position like this, white has a rook and an extra pawn.
The pawn is only one square away from getting to the end of the board. When a pawn gets to the end of the board, it promotes. It becomes a more powerful piece than a pawn. It can become anything other than another pawn, it has to become something other than a pawn, or a king. There can only be one boss on the board at any one time.
Most of the time, pawns promote to the queen, which is the most powerful piece. In this position, if white advances the pawn and promotes it to a queen, the queen will be attacking the king. That'll be a check. The king cannot go four squares and capture the queen. There's nobody that can block and the rook prevents the king from escaping, so this would be an example of pawn promoting leading to checkmate.
There are times, though, that you might wanna promote the pawn and make something other than a queen. For instance, here, white has a king and two pawns, black has a king and a queen. The king and the queen are usually much more powerful than the king and the two pawns and if it was black's turn to play, black would just take this pawn and eventually, the king and the queen would beat the king and the pawn. But if it's white's turn to play here, he can win by using something called under-promoting.
Now, most people would advance the pawn and promote to a queen in this situation 'cause the queen is the most powerful piece, but here, black would then be able to bring his own queen down to C1 and say checkmate to white. So, promoting to a queen would not actually help white. But if white, in this position, promoted to something less than a queen, in this case, a knight, the knight would be forking, attacking both the king and the queen at the same time, the king would move, the knight gets the queen check, the king can attack the knight, the knight escapes, but eventually, the king, the knight and the pawn will defeat the king. The king, the knight and the pawn will work together to eventually turn this guy into a queen and then, the king the queen and the knight will eventually checkmate black. And I hope you now understand pawn promotion.