January 2002 Update - 1.e4....
I received an interesting email from Doug Schwetke, pointing out that the variation 1.e4 Nf6 2.e5 Nd5 3.c4 Nb6 4.d4 d6 5.f4 dxe5 6.fxe5 g6 was neither on the site or my recent book for Everyman, and kindly attaching a file of games. Accordingly I have given this line some coverage in this month's update.
Black's main idea is to undermine White's centre with ...c7-c5, and a radical way for White to prevent this is to play c4-c5 himself (as in Rigo-Andruet, JAN02/01). The disadvantage of this being that it makes a 'hole' on the d5 square. Can Black exploit this or will he suffer from permanent cramp?
White habitually plays an early Nc3, but I have my doubts about whether it has to be played early on. In Pinchon - Timmermans, JAN02/02, we see White focus on the development of his kingside, but he should play Nc3 on his 11th move, in my opinion. Another Four Pawns habit is to defend the d-pawn with Bc1-e3, but here he must be ready to meet ...c7-c5 as in Fish - Sharp, JAN02/03. As for natural development, that doesn't work either with Black obtaining typical counterplay in Parma - Schiffer, JAN02/04.
Last but not least, the game Riedel - Schneizer, JAN02/05, transposes into the 6...c5 7.d5 g6 variation. Actually it features an interesting alternative to the 12...Bg4 played in Volzhin - Svechnikov (AV209 SEP00).
All in all it seems as if there is plenty of mileage in 5...dxe5 and 6....g6, and it has the benefit of avoiding the massive amount of 4 Pawns theory.
If your opening repertoire needs freshening up, you could do far worse than search some of Bent Larsen's old games for ideas. An independent and original thinker, the great Danish Grandmaster has original twists and turns in almost every opening. The Exchange Caro is a line I often recommend to my students and in Larsen - Seirawan, JAN02/06, we see a familiar Larsen twist with 4 c3. He does not seem to be at all concerned by the fact that he is not preventing Black from developing his bishop on f5.
Games 7-10 inclusive feature more tonic for the Exchange Caro. The pavlovian development of White's bishop to f4 is not his only option, and independent thinkers have been toying with 6. Bg5.
At club level this is particularly interesting because it is often met by 6...e6. Another unthinking move which avoids doubled pawns but hems in the bishop on c8, see , JAN02/07.
If there is an argument against 6.Bg5, it is probably the immediate 6...Ne4 as in Weenink - Gudju, JAN02/08. White can win a pawn but there is dangerous compensation. My own preference would be for one of White's 7th move alternatives.
Does 6.Bg5 threaten to capture on f6? Probably not, at least when Black is able to recapture with the g-pawn. But after 6...g6 it is interesting, as in Bhend - Ciric, JAN02/09. The most popular answer to 6.Bf4 is 6...Bg4, and in Rausis - Berg, JAN02/10, we get similar play after 6.Bg5. But one finesse to look out for is the fact that ...h7-h6 by Black creates a weakness on the kingside, and the Rausis plan of Kh1, Rg1 and g2-g4 could be very effective.
Keep your questions coming in, I'll attempt to address the most popular issues.