A few weeks ago, in a post titled Comments on Chess960 Opening Theory, I noted that an 'approach to chess960 opening theory using the "Queen starts in the corner" concept seems promising'. In this post, I'll develop a framework to document that concept.
Although there are 960 different start positions, there are many similarities across those positions. For example, any start position with a Bishop on the a-file has certain characteristics in common with all other positions having a Bishop on the a-file, and those positions have the same general characteristics as positions with a Bishop starting on the h-file. The same is true for a Knight starting on the b- or g-file, for a Queen on the c- or f-file, or for any combination of piece and start squares. (Because of the differences in castling O-O vs. O-O-O, the King is more complicated, but I'll deal with that separately.)
The table below maps the start positions for each of the five pieces against each of the four types of files. Since the King can't start in the corner, that possibility is excluded. A quick count or calculation (5 x 4 - 1) reveals that there are 19 different piece/file relationships to consider.
Table 1 : Pieces and Possible Start Files
One of the problems with algebraic notation is a lack of nomenclature for files that are related by their chess board geometry. This is useful when speaking about chess principles that apply equally to the left side and right side of the board, like 'in the opening, aim to develop your Rooks on the center files', where the term 'center files' means the d- & e-files.
In traditional chess (SP518), the generic names for files aren't particularly useful in the opening, but become more useful in the endgame. The complications created by the presence of a 'Rook Pawn', a phrase taken from the older descriptive notation and referring to Pawns on the a- or h-files, are one well known example, as in 'Bishop of the wrong color vs. Rook Pawn', but there is no real equivalent for positions with Pawns on the b- or g-files -or- on the c- or f-files.
In chess960 the concept of related files is more important in the opening. A discussion of positions where 'Queen starts in the corner' refers to the entry (or cell) in the table which is the intersection of the row for the Queen and the column for the a/h files. I've marked it '(!)' in the following version of the same table.
Table 2 : Pieces and Specific Start Files
The cells marked '(*)' represent starting positions where the pieces have the same considerations as in traditional chess (SP518). For example, a Knight starting on b1 (represented by cell 'N:b/g' in the table) is developed most often to c3, less often to d2, and least often to a3 -- ditto for the other Knights. The cell 'B:c/f' offers the choice between developing a Bishop on its 'long' diagonal (d2, e3, f4, g5, h6 for a Bishop on c1) or on its short 'diagonal' (b2, a3), where the development to b2 is a 'fianchetto'.
Chess players learn the '(*)' concepts early in their education and come to know intuitively the trade-offs when developing those pieces. This is one reason why other chess960 positions look strange and why they can, at first glance, seem unharmonious.
Each of the elements of non-SP518 start positions, like Q:a/h (Queen in the corner), can be characterized using similar reasoning, then documented. An anomaly that I pointed out in a previous post (see 'Table: Chess960 Start Positions per Piece per File' in Introduction to Chess960 Geometry) is that there are more positions with R:b/g than there are with R:d/e.
In future posts I'll discuss the non-traditional positions, pieces, and start files, with examples from real games.