Largest possible number of legal moves

All Things Chess
1

Time for a CONTEST !!

Find a legal position in which the number of possible legal moves is as large as possible.

Winner is the person who submits a position with a larger number of possible legal moves than anybody else.

By “legal position” I mean a position which can be reached from the standard starting position with a series of legal moves.

Promotions only count once. For example, if white can play either c7-c8=Q, c7-c8=R, c7-c8=B, or c7-c8=N, that counts as only one legal move, not four.

My entry in this contest is the following position, with white to move. If I’ve counted correctly there are 186 possible legal moves for white.

I’m pretty sure this is a legal position. White’s last move could have been, for example, Qa3xRd6, and black’s reply could have been Kd8-e8.

Bill Smythe

2

Move the Bc1 to b8 (adds one B move, eliminates two Q moves, adds four Q moves) a7 is the same (adds three B moves, eliminates two Q moves and two rook moves, adds three Q moves, adds 1 K move)
Move Bf1 to g8 (adds two B moves, eliminates two Q moves, adds three Q moves, adds 1 K move)
Move the Nb1 to a8 after moving the Bc1 to a7 (eliminates one N move and one Q move while adding three Q moves and two R moves)
Move the Ng1 to f8 after moving the Bf1 to g8 (eliminates two Q moves while adding one N move, two R moves and two Q moves)

That allows adding 13 moves overall.

I do see multiple spots for the king that would add one net move.

3

Hmm, nice. That brings it up to 199 total.

Oh, you mean the white king. That would be great, if it’s true. It would break the 200 barrier. But don’t forget you’re also losing one more king move, namely O-O.

Bill Smythe

4

How many illegal moves could be generated from the starting position? If each illegal move would require adding two minutes to the opponent’s clock, how many hours/days/years would the game last? Of course, after the third or fourth offense, a TD could impose a harsher penalty, but if he/she is less draconian, then the silly game might trend toward entropy.

5

I missed castling as an additional move, so you already have that one more.

6

Maybe move the white rook from a1 to a5?

7

OK, good.

Hmm, let’s see. You lose one Q move (from f5), but you gain two (from d1 and b2) Nice.

Bill Smythe

8

Move Black K to h8
Remove Black P e7
Add Black Ps on g7 & h7
Move White Q g7 somewhere (e8?)

Too lazy to count, but I think this is more.

White to move, of course :smiley:

9

deleted bad diagram

10

Illegal position, eh? (My previous suggestions were bogus because Black had no legal moves that would reach the position. I also deleted a suggestion that proves my inability to count on my fingers.)

Jeff Wiewel pointed out one remedy, which costs one move.

This seems like an obvious task that others must have tried before.

11

I think this adds one square, net.

See y’all at Reading Terminal Market.

12

Moving the knight from a8 to a6 adds two queen moves to a8 (from e8 and b7), but subtracts three queen moves to a6 (from b7, d6, and c4) and one rook move to a6 (from a5), net loss two. It adds two knight moves net (lose 2, gain 4). So it breaks even.

You put the pawn, which had been moved to h6, back on h7. The problem now is that Black has no legal previous move.

13

Add a black knight on a1 (having moved their from b3). That allows legality of the position and does not take away any moves.

14

Doesn’t that add two N moves, but take away 2 Q moves and 1 R move?

15

No. Either Q or the R can capture the black knight.

Alex Relyea

16

OK, let’s total this up. It’s been a while.

Qb2: 18
Qb7: 16
Qc4: 23
Qd1: 14
Qd6: 22
Qe3: 22
Qe8: 15
Qf5: 23
Qq2: 17
Ra5: 8
Rh1: 8
Ba7: 4
Bg8: 4
Na6: 4
Nf8: 4
Ke1: 5 (including O-O)

total: 207

Question 2: How many of these moves are checkmate? How many are stalemate? How many are neither?

Question 3: White to move, black to helpmate white, what is the minimum number of moves in which this is possible?

Bill Smythe

17

Six checkmates: Qxh7, Rxh7, Qb7xg7, Qb2xg7, Qgxg7, Ng6
Zero stalemates (if the knight was not on a1 then Bxh7, Nxh7, Rh6, Qeh6 or Qdh6 would have been stalemate)
With 207 moves, 201 are neither checkmate or stalemate.

Quickest helpmate of white is:

  1. Qed2 Nb6, 2 Bf2 Nd4, 3 Qbe7 Nxf5, 4. Qee2 Nh4, 5 Rf1 Nxg2#

    PS None of white’s 126 moves parries the checkmate.
18

Actually, I think I have asked that very question, somewhere in these forums, a while ago, but I don’t remember who won the contest.

Bill Smythe

19

There’s a position with over 200 legal moves for White, but White has 9 queens, so it is not one that is likely to ever occur in a real game.

20

I found it!

Bill Smythe