Generally the critical cross-road in the Classical Dutch is considered to arise after these moves: 1.d4 f5 2.Nf3 Nf6 3.g3 e6 4.Bg2 Be7 (the Modern Dutch Stonewall is characterized by the move 4...d5 followed by ...Bd6; the advantage is a more active employment of his dark-squared bishop and the disadvantage is that Black s reveals his central formation earlier) 5.0–0 0–0 6.c4 d6 7.Nc3 (Dia)
In this position Black's main moves are 7...Ne4, 7...Qe8, 7...a5 (all examined in Simon Williams' Play the Dutch played by strong players and in general quite well researched) and 7...c6 (which has been played by Saemisch among others but seems unfashionable). None of these moves are developing moves in a strict sense but they all to some extent prepare queenside development, prepare ...e5 or prevents e4.
the picture is entirely different. Black's main options are 6...d5 - Botwinnik's Stonewall which sets up a relatively static centre and 6...d6 - the Classical Dutch (aka. the Ilyin Zhenevsky variation) which keeps the central pawns fluid (but generally prepares ...e5).
However there is also another relatively popular option - Alekhine's idea 6...Ne4!? which delays this decision. This system too is examined in Williams' book. Black's main idea is to meet some of White's developing schemes with ...d5 and others with ...d6. Another benefit is the fact that Black doesn't allow b4 (6...d6 7.b4!? is quite an important little line, scoring considerably better than 7.Nc3).
Another respected 6th move with similar motives is Bellin's 6...c6!? which has slowly increased in popularity for at least 15 years. This line has been played by Short, Larsen, Smyslov and Bronstein among others and is discussed in Giddins' excellent 'How to Build Your Chess Opening Repertoire'.
These by no means are easy lines to play for Black. Not only does he delay development but he also needs a good general understanding of the Dutch. In order to play the position well, you not only must know when to go for a Stonewall set-up with ...d5 and when to go for a fluid centre with ...d6. You also must be able to handle both kinds of position well!
The obvious question is: What about 6...Qe8!? (Dia) and 6...a5!? (Dia).
None of the moves have been tested in modern grandmaster clashes. Actually there are relatively few practical examples altogether - I find only 99 games with 6...Qe8 and 30 games with 6...a5 in MegaBase 2009. Obviously both moves can transpose to standard lines after 7.Nc3 d6 so the two principal questions are now:
- Can and should White avoid 7.Nc3 d6 which would transpose to the 6...d6 7.Nc3 a5/7...Qe8 lines?
- After 7.Nc3, can Black give the game an independent twist with an alternative to 7...d6 (or are these moves just move-order tricks avoiding the 6...d6 7.b4 option?)?