Comments/Ratings for a Single Item

[23] All squares are essentially equal, there is no terrain to consider.

This criterion draws a line to war simulation games, where land, water and cities play an important role.  

Xiang Qi mildly violates this one.

> 22. Pieces belong to a player.

Good point. It did not occur to me to mention this, but for me it carries as least as much weight as any other of the characteristics I mentioned.

OTOH, I would not put any weight on things like 'pieces should move like Chess pieces' or 'Can be played with Chess board and pieces'. This seems to single out a specific variant (namely Mad Queen) as overwhelmingly more important than the others. While IMO it is just one of the many Chess variant, and not even the most popular one on the planet.

Furthermore, a point system should take into account that the characteristics are not just boolean all-or-nothing things. For my perception of Chess-likeness it definitely matters if the rules are mildly violated (e.p. capture and castling in Mad Queen), or badly violated (e.g. almost no piece captures by replacement, as in Ultima). So the question is more if the typical behavior satisfies the requirements, rather than that no exception at all is tolerated.

The concept of 'recognized variant', in the sense of very widely played, should probably play some rule too. For instance, if a game is on the edge w.r.t. the number and severity of how it violates the defining characteristics, it should never be pushed over the edge based on whether it also allows e.p. capture or not. This particular transgression of the replacement-capture requirement should be designated 'acceptable' because it is so common (which no doubt can be traced back to the popularity of the recognized variant that incorporates it.)

There also seems to be need to weight the opposite: likeness to very popular games recognized to be not Chess variants. If Checkers would be recognized as an independent game, (which I think the vast majority of people would agree on), I would be inclined to reject games that are more like Checkers than like Chess, even if in an objective measure they are closer to Chess than some other variants which do not happen to be close to any other recognized game either.

Good game design is ultimately a matter of generating appropriate reactions in players.  Analyzing how people feel about games they've played (and why) can suggest new ways for a designer to elicit (or avoid) particular reactions.  Making lists of things that contribute to an overall 'chess-like' impression seems like a pretty reasonable thing for chess variant designers to spend time doing.

Assigning actual point values is probably reaching beyond the available data, though.  Verify your models carefully before you trust them.

David Howe made a list of some features of a chess variant game. I am going to list a few more (but without assigning points to them):

12. Game does not involve physical dexterity, drinking, etc, so it could be put into a computer; but no computer is required to play game in general.
13. Real time taken does not affect the rules of the game (except the tournament rules, which might give you time limits, and stuff like that).
14. Board is finite and the geometry/topology of the board won't change during the game.
15. The game is played using standard chess pieces and chess board.
16. There is no decision other than the movement of the pieces.
17. Pieces moves like chess pieces can move.
18. You will normally have a choice of which piece to move and which way to move it (within the restrictions of the rules).
19. Game has well-defined ending condition.
20. You win, or lose, or draw; it is not ambiguous and you do not win by a number of points which can vary.
21. The different function of different pieces is mostly only their difference of movement.
22. Pieces belong to a player.

Some games might partially or almost have a property listed but not entirely, or have slight variations on the properties listed (for example, more than one royal piece, or some pieces captures by displacement and others don't, or special circumstances in which you can move more than one piece, etc).

I think Nemoroth is a chess variant: Humans is like the pawns (weakly, more of them at the start, cannot retreat, and promotes); uses equal sides; different pieces of different function; etc. But in chess the pieces just move differently while in Nemoroth their other functions also vary a lot. There are many other differences too rather than make them like other chess variant games.

P.S.: You still did not fix the bold footer (there is an extra B tag which should be removed)

David, I also find the 'point-count' classification interesting and possibly fruitful.  One interested in games in general might establish 'point-count' characteristics for other types of games, and then for those games that are ambiguous, one could perhaps, for instance, compare the various 'point-count' analyses of a difficult case like Nemoroth to decide whether it is more a Chess variant or a Fox-and-geese variant.
One of the characteristics could be, as trivial as it sounds, does any game in question take advantage of the physical nature of a chess set to define or clarify aspects of its own rules?

Here's my take after a little thought. The point assignments probably need work.

A game which is a form of chess, is one which includes all of the following properties:

1. A game of movement and capture, rarely of placement (2 points)
2. Bilateral symmetry and equality of material (1 point)
3. Functionally differentiated pieces (2 points)
4. Capture by replacement (1 point)
5. Win by capturing a definitive singleton (royal piece) (3 points)
6. A Turn-based game (1 point)
7. A Two-player game (1 point)
8. A game of Complete information (1 point)
9. Played by moving pieces between discrete positions (2 points)
10. The players can move one piece per turn (1 point)
11. One piece type is more abundant than the others, quite weak, moves uni-directionally and can promote (1 point)


[1-5 (but not the point system) taken from: Parlett, D. S. (1999). The Oxford history of board games. Oxford: Oxford University Press. p. 277.]

[6-11 (but not the point system) taken from H. G. Muller's post on chessvariants.org commenting system.]

Suggested terms:

Chess-game: 16 points (all properties)
Chess-like game: 10-15 points (many properties)
Chess-related game: 4-9 points (some properties)

Note that many chess variants are (according to this scheme) chess-like or chess-related games.

Examples:

Go                = 0 + 1 + 0 + 0 + 0 + 1 + 1 + 1 +0/1+ 1 + 0 = 5/6
Checkers          = 2 + 1 + 0 + 0 + 0 + 1 + 1 + 1 + 2 + 1 + 0 = 9
Losing Chess      = 2 + 1 + 2 + 1 + 0 + 1 + 1 + 1 + 2 + 1 + 1 = 13
Extinction Chess  = 2 + 1 + 2 + 1 +0/1+ 1 + 1 + 1 + 2 + 1 + 1 = 13/14
Ultima            = 2 + 1 + 2 + 0 + 3 + 1 + 1 + 1 + 2 + 1 + 0 = 14
Progressive chess = 2 + 1 + 2 + 1 + 3 + 1 + 1 + 1 + 2 + 0 + 1 = 15
Grand chess       = 2 + 1 + 2 + 1 + 3 + 1 + 1 + 1 + 2 + 1 + 1 = 16

Is this chess?

    
http://www.chessvariants.org/index/msdisplay.php?itemid=MSchesimals:auto

I agree that we should look for a continuum; probably the best approach is to decide upon several factors (like the Muller 7) that can be reasonably easily computed for different games.  What is perhaps lacking from the Muller7 is a measure for which aspects are most important (perhaps it is just equally weighted, but I think they should not be).  The ultimate goal (IMO) is for the measurements to come as close as possible to our collective opinion of what is 'chesslike'.  (See also Joyce's 'Chess Space', on the wikidot as well as in some comments here I believe.)

A couple of examples that might be helpful to keep in mind:
1) games using chess pieces that are not chesslike in gameplay: Joust (not very chesslike), or Knightsweeper (not chesslike at all) [both on this site]
2) Lennert's 'For the Crown' (half chess, half something else)
3) already mentioned, but Go and Checkers (and their variants; Gess perhaps?)
4) other games that are clearly not 'chesslike' but that have similarities should be noted; these might help weight the characteristics.

If 'chesslike' is not well defined enough, maybe it's useful to think in the following way.  If you wanted to tell a friend about this game, is it easier to say 'It's like chess, but...' or just to start from another game (or from nothing at all)?  Of course, some games will be equally easy to start from chess or to start from some other game (e.g., For the Crown seems easier to describe as 'like Dominion, but with chess', but maybe for some people, 'like chess, but with deck building' is better).

Oh, and maybe it's good to distinguish between a theoretical classification and guidelines for this site.  I tend to think this site should be very inclusive, but am happy to draw the boundaries tighter in theoretical talks.

IMHO, Muller's 7 criteria look quite useful for estimating how chess-like a game is--a continuum, rather than a binary is/isn't categorization. They would provide a conceptual framework for observations such as (to intentionally cite an extreme example) Capablanca's Chess is more chess-like than the Game of Nemeroth. Where the line is between chess variant and non-chess games cannot and indeed need not be determined exactly. The question is, is a given game chess-like enough for it to be useful to consider the game a chess variant--can a useful number of Chess concepts be helpful in playing and analyzing the game?

But drawing lines can be fun and useful if it isn't absolutized. Approached in a spirit of 'reasonable people can disagree', everyone should be free to chime in.

As a starting point for looking at some edge cases, I offer my own game Wizards' War for consideration: 
1. It has royal pieces, though capturing them is not the only method of victory.
2. It is entirely pawnless (in the Muller sense--many games are pawnless in the sense of 'this game has no piece that moves like an FIDE pawn').
So is it a chess variant or not and why? Bonus points for citing games that are clearly but not hugely more/less chess-like.

'It seems you want to erode the meaning of 'Chess variant', to become synonymous for 'board game'.'

I don't have any 'want' whatsoever, in this case.

No.

Any one-player board game such as a puzzle or solitary connection game is definitely not a chess variant.  Therefore, chess variants, even by the most holistic, responsible definition, are merely a subset of board games.
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'I think it is very good to have language where you can make a distinction between Chess (variants), Checkers (variants), Go (variants) etc.'

I agree that distinctions in language are useful.  I also think it is equally important to recognize overwhelming similarities that are often overlooked, disregarded or trivialized.

It seems you want to erode the meaning of 'Chess variant', to become synonymous for 'board game'. I don't see what is to be gained by stretching the meaning of a term to cover something for which there already exists a perfectly good word. It gives me a definite Smurfish feeling.

We could even expand the meaning further. Why require a board, when a meadow could do? Why require turns or players? Or a winning condition? A cow is also sort of a Chess variant, right? It also moves on a 2D plane...

I think it is very good to have language where you can make a distinction between Chess (variants), Checkers (variants), Go (variants) etc.

Although I regard Muller's list of seven desirable conditions as an excellent guideline (on most points, in my opinion) for being conducive to the possibly of creating a high-quality chess variant (which is pertinent to the title of this thread), the present question as to what defines a chess variant yields fewer conditions.

Generally, if a game has a board (2-D or 3-D) with spaces (e.g., square, 
triangular or hexagonal in 2-D), some (not necessarily all) mobile pieces
that occupy those spaces, a turn-based move order [Note:  I've never been able to successfully devise a simultaneous move game.] implying two or more players and a winning condition, it is a chess variant.  Even capturing (by various means) is not mandatory to this definition.  Also, having different piece types and abundances is not mandatory although both are strongly advisable since a lack of variety diminishes tactical depth.

So, chess variants actually include many classes of games that are not popularly classified as such.  For example:  connection games, war games, checkers variants, shogi variants, ultima variants, etc.  Furthermore, the hybrid usage of dice, cards, etc to render the overall game one of imperfect information is not prohibited.

Chess-variant should be a rather loosely- defined concept; trying to make a strict definition will always lead to unnatural inclusions or exclusions. The defining characteristics of 'greater Chess' are IMO:

1) Turn-based two-player game with complete information
2) Played by moving pieces between discrete positions ('board squares')
3) The players can move one piece per turn
4) Pieces capture by replacement
5) Many different piece types
6) One piece type is 'royal', the loss of which ends the game
7) One piece type is much more abundant than the others, quite weak, and moves irreversibly and can promote.

Violating one or more of these rules doesn't necessarilly immediately diqualify a game for being a Chess variant. But if you violate a rule very badly (e.g. win by total extinction, in stead of check-mate, as in Suicide Chess), you'd better follow the others to the letter, or you are in trouble. So Suicide is OK because it does everything exactly the same as FIDE Chess (which is a recognized Chess variant, so its tiny transgressions of rule [3] and [4] through e.p. capture and castling are forgiven) there is little doubt it is a Chess variant.

So things like Turnless Chess (badly violating [1]), Marseillaise Chess  (badly violating [3]) are still well out of the danger zone. DarkChess and Kriegspiel (bad violation of [1]): OK. Ultima I am not so sure about. I am inclined to say 'no, too outlandish!' on that one. Although it does have a royal piece, which even moves like an orthodox King. But the 'Pawns' are not irreverible, capture is almost exclusively other than replacements. So that is two badly violated rules. And indeed the game does not 'feel' like Chess.

Extend Nomic's methodology to analysis, http://www.chessvariants.org/multiplayer.dir/nomicchess.html, and realize it is matter of degree, not all or nothing inclusion. If having royalty is immutable per Nomic 100s, then that is the definition. But if royalty is mutable rule too, then to determine is how many steps removed a given CV is from a standard.  So each CV is CV of x-degree by how many Mutators it takes to get back to the original. What is a CV gets discussed once every couple years. Other unconventional win conditions are in Maxima, Anti-King, Betza's and Parton's Racing games.

I don't buy it. By that definition, it seems that Descent: Journeys in the Dark is a Chess variant, because the heroes win (in most scenarios) by killing a specific boss monster, but Losing Chess is not, because the victory condition is extinction, and Nemoroth also is not, because the victory condition is stalemate.

I would say rather that being a 'chess variant' is a matter of family resemblance. Games that resemble Chess more closely than they resemble other well-known games are deemed chess variants. Checkers escapes being termed a 'chess variant' mostly because it is, itself, well-known; someone with long familiarity with Chess who was introduced to Checkers for the first time could plausibly decide it was a chess variant.

This resemblance is generally a result of having several key mechanics in common with chess (including a uniform tesselated playing area, armies of pieces with different movement capabilities, alternating turns in which a single piece belonging to that player can be moved, capture by displacement, and a single royal piece whose checkmate or capture ends the game)--and also NOT having too many key mechanics that Chess lacks. But no single feature is either indispensible or verboten; it's just a question of whether the game, taken in whole, reminds us of Chess more than it reminds us of something else.

'The single defining quality of 'Chess' is that

the winning condition is predicated on one (the royal) of two (royal and non-royal) classes of pieces

If a game exhibits this quality it is a Chess Variant, if it doesn't it isn't.'

(http://chessvariants.wikidot.com/chess-variants)

There is a question about the two essential elements of chess variants. 
In some chekers variants a cheker can promote into a king, then we get pieces with different powers. This is one of two most widespread and important similarities. But chekers is still not some chess variant. We can even desighn a chekers variants with king in initial setup. Is this a chess variant?
Is the breakthrough game Camelot a chessvariant? It has pieces with different powers.
An elimination game with pieces of all pawns (or rooks, or queens) and a chess board is also called a chess variant. The reason is probably that pawn is derived from chess.
Once again, are these two most widespread and important similarities essential to chess variants?