Enter Your Reply

Interesting observation, George. Putting the numbers together like that
certainly shows a strong trend. With the caveat that this result is for 2D
games with board sizes very near 8x8, the result may tell us something
interesting about chess in general. A number of very different people have
contributed to this project in one way or another. That the piece-type
density falls out so close to 10% in all these games, even when the pieces
themselves may be very different from FIDE standard must mean something,
but what? 

It does seem as if most variants follow this 10% rule, but it could be
equally true that 5-10 piece types in a chess variant is the default human
standard, that we find a handful or two of piece kinds just about perfect,
regardless of size. Then we could quantify the rule as: 10 +/- 5 is the
number of pieces humans like in a chess game. In that case, I suspect it
would be a playability issue. Humans can keep only so many things in mind
at one time. As boards go to significantly larger sizes, they become less
playable if a 10% ratio is maintained. Some of the shogis should illustrate
this. 

But turn it around and look at smaller boards. Many smaller games reduce
the total number of pieces considerably, but the piece-types by much less.
Often one piece only is dropped. And some keep everything on a much smaller
board. An excellent example of this is LL Smith's One Ring Chess. With 32
squares, it has all 8 standard pieces and 4 pawns/side, jumping the ratio
to 20%. 

If the second idea is right, an examination of very large and very small
chesses should show them not holding at 10%, but 'cheating' toward a
particular [small] absolute number of pieces.