I found this to be a funny question as I’ve never thought about it! I mean just imagine who would actually choose to keep a pawn on an actual game, it just doesn’t make sense.
The pawn is not only the weakest unit in Chess but also the one that cannot move to other directions than the column it resides in.
A pawn cannot remain a pawn once it reaches the other side of the board where it is obligated to undergo a promotion.
The promotional rule states that a pawn shall be converted to any of the chosen pieces of the player’s discretion, well, every piece except the pawn.
Probable reasons why you can’t keep the pawn
There just aren’t any real beneficial reason to keep a pawn in its current form and avoid promotion.
If a player badly needs to keep a pawn in the game, then he/she can just choose to avoid moving it in the first place, there’s just a lot more sense to have a more useful and powerful piece that can be used for long term.
In fact, the pawn will be much more useless than ever at the last rank since it loses its ability to capture.
As you may know, a pawn can only capture on the two upper sides on the column it is facing, this is very unfortunate as there is no such thing as upper side on the last rank! since it is the uppermost segment of the board.
Adding to this, a pawn on the last rank can’t even be used to achieve a closed position by blocking.
A pawn on a regular file can close a position and prevent other pieces from accessing a particular square by using key advances to create a blockade.
Even a bishop and a pawn can create that blockade, usually to prevent King’s advances or to prevent a rook’s influence on a particular file or rank.
b.) Convoluted rules
Not only is it not necessary but also it will create a heck lot of problems in physical chess.
Like in a simple rule of touch move, how are you suppose to tell that a player is going to promote and not just keep the pawn?
A player might unknowingly advance a pawn in excitement for a promotion only to be called out by the opponent!
This is a claim that is very hard to disprove unless a recording has been put to place and if you’re not a professional which most chess players are, then you’re in trouble.
A player can even make accusations even when if no such thing occurs.
That’s how convoluted this is, anyone could put up a fight and cause a ruckus that even the arbiter might not know how to solve.
And you think ” that’s probably unlikely since most players are honest”.
You couldn’t have been more wrong! players are desperate for victory when the stakes are high.
It’s rare to find a considerate individual that cares about the true results, you know, someone like me—maybe.
But anyway, there’s a lot of greedy players out there that will complain about any single mistake they can find, this single inconsistency can actually be a huge blunder that could cost the game.
There are some situations in Chess where bringing a Queen is not enough to win the game.
This usually happens when the promoted piece is out of reach from the game’s crucial squares (areas where actions actually occur), while at the same time, having the King open to be caught in some sort of mating attack.
This is a special scenario since the Queen normally had very long reach that extends to the other side of the board, but this is true for the other Queen as well.
A checkmate might occur much faster than you’d expect when there’s a mating net (forced checkmate), where no available move that can save the King.
Not only that, the opponent can place pieces in particular squares that boxed the Queen out, especially since it will be emerging at the last rank of the board where there are no action.
You might’ve experienced this on your own games, that well-placed minor pieces can outmaneuver the major one, I sure have!
A change in rules means a draw can be done in such positions, and we don’t like that (nobody likes draws), the inability to keep a pawn might’ve been put in place to prevent stalemate tactics that’s already growing within the Chess community.
Why you shouldn’t worry about it.
a.) Piece value
Pawns have lowest value unit in chess and for a good reason.
They are slow, one tile moving scraps with limited capture capabilities and movement directions.
As they can only move in one direction which is the file they are currently at, this makes them easy pickings for any higher-valued piece as they don’t much have options to evade the attack.
Adding to that, promotions usually occur during endgames where everything on the board matters.
Choosing to keep a pawn when you can promote a Queen can be considered dumb in some ways, as the difference in power is so high it is not even comparable.
b.) Under promotions
Piggybacking from the previous concern, have you ever thought why professional players in some cases refuse to bring a queen to a game and instead opt for a Knight or rook?
Because of their special abilities!
A Knight has that weird movement capability where can deliver checks during a promotion, especially when your own king is about to be checkmated.
The knight can then maneuver itself to be useful in some ways to execute a fork or increase drawing capabilities via some known chess studies.
A rook on the other hand is usually brought to prevent a stalemate where the diagonal capture of the Queen just prevents the King from making a move, therefore causing a draw.
In these cases, a rook is the better option since it’s almost as good as the queen in terms of power, but also is limited enough to not cause a stalemate.
The pawn offers none of these perks—none at all, it wouldn’t have mattered if it was the unit with the lowest score if it can change something in the game.
But no, it would just be a helpless target in the most crucial stage of the game (endgame) where promotions usually occur.
Abuse only work in games between beginners if even just one of the players have a vague idea of the game’s rules.
There’s a lot more opportunity to make up an unfair rule that is only beneficial for a single player.
Such make-up rules possible would be
“You cannot promote a piece that hasn’t been captured yet! So that must remain a pawn”, “You have failed to call the name of the promoted piece during the advance! means you keep the pawn as it the last one touched”, or “You failed to change the pawn before hitting the timer therefore you keep the pawn”.
See? the timer thing might’ve caused some penalty, but definitely not keeping a pawn to be promoted, which is very unreasonable.
All of these have similar aspects to them in one way or the other, and again would only work on beginners.
Those who have known the game’s rules would never fall for such a trick.
But if you’ve learned anything in bet games, it’s that everything is possible:) so this could be a problem.
In conclusion, keeping a pawn does not really offer any merit in a practical game and instead, pave way for opportunities of abuse in game’s rules that could rob someone of a victory.
This actually becomes it a sort of protection that does not allow the action to exist, in order to make the game more decisive and interesting, I sure think so!