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Why is 4. e3 preferred over 4. e4 in this line of the Slav?

 rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1 
 1. d4 d5 2. c4 c6 3. Nf3 dxc4 4. e3

I would expect 4. e4 to be preferred, as it grabs more space in the center. The line usually continues 4. ... b5 5. a4 and if 4. e4 had been played, this would be very similar to some QGA lines, with a pawn structure identical to those QGA lines.

1 Answer 1

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It seems that the center becomes weak after 4. e4 and white has trouble regaining the pawn as a result. For example,

 rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1 
 1. d4 d5 2. c4 c6 (2. c4 dxc4 3. e4 Nf6 4. e5 Nd5 5. Bc4 Nb6 6. Bd3 Hc6 7. Ne2 Bg4 8. f3 Bh5 9. Be4) 3. Nf3 dxc4 4. e4 (4. e3) b5 5. a4 (5. Nc3 Nf6 6. e5 Nd5 7. a4 e6) Nf6 6. e5 Nd5 7. axb5 cxb5 8. b3 e6 9. bxc4 bxc4 10. Bxc4 

In this position specifically, white has wasted two or three more moves trying to regain his lost pawn than he would have with 4. e3. As you can see, playing 4. e4 instead of 4. e3 gives black the opportunity to gain a tempo after 4...Nf6, which allows him time to equalize quickly by either defending his queenside pawns, which are his main weakness, or giving the pawn back and gaining massive piece activity and weak d4 and e5 pawns to target in the middlegame.
This is one line, but there are also lines in which black's light-square bishop gains activity down the a8-e4 diagonal, or in which white can only regain his pawn at the expense of losing both of his center pawns. If white plays 4. e3 instead of 4. e4, he has the advantage of still attacking the c4 pawn while also not compromising the integrity of his pawns. 4. e4 is a massive overextension of the center pawns that will be difficult to defend both now, and in the middle and endgame
After 2. e4 in the QGA, the pawn center is usually attacked by black, but it is also fairly defendable. This is because, as you probably know, protecting the c4 gambit pawn as black is usually a terrible idea, mainly because he must first protect the pawn with b5, then spend another few tempi protecting his b5 pawn, which can allow for white to gain a massive attack. As a result, unlike in the Slav, white doesn't have to bother recapturing the c4 pawn, because he knows he can do so at any time. Because of this, white can spend more tempi building up a center with 3. e4 and protecting his center pawns while also putting his pieces on nice squares.
Let's go back to the Slav with 4. e4 that you described. Again, the white center pawns are objectively pretty weak, and black can easily target them. The difference now is that black just has to play b5 to protect the c4 pawn, and not have to spend additional tempi to protect b5 from attack, as it is already defended by c6. Thus, compared to the QGA, protecting the c4 pawn becomes a real threat from white's POV, as black can do it easily and without too much loss of tempo. So now, white must defend his pawn center, which is still weak, while also trying to recoup the pawn on c4. (It's also important to note that the b5 pawn restricts white's knight, because if black plays ...Nf6 attacking e4 and white responds with Nc3, then b4 is now also a threat).
If you look at the variation I posted in my answer, white gets overloaded from those two tasks fairly quickly. White is basically forced to give black's knight a nice blockading outpost on d5, making his center pawns basically dead in the water, while also running the risk of not ever regaining the c4 pawn. So, in order to actually regain the pawn white has to play e3 as not to overextend himself. While white has pawns in the center, they are actually very weak, and looking through the lines below, he has nothing to show for his pawn center and all his pieces either on the back rank or doing absolutely nothing. Now compare this to a sample QGD line with e4 that I have also put down below. Whereas white does have a slightly weak center, 1) he can easily protect it and 2) his piece activity and coordination more than makes up for it either way. Notice how in the QGA position, all of white's pieces are poised well for an attack on either side, while in the end Slav position below, the center looks nice and the pieces are out, but the pieces aren't actually achieving any purpose and the d4 pawn is going to be targeted in the long term. It's also important to note that black gets an outside passed a-pawn from this, which may be useful in the endgame.
Basically, white can afford to play e4 and protect his center in the Queen's Gambit Accepted, while in this Slav line, white is overextending himself if he plays e4 and gets nothing from putting his pawns in the center

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  • Sorry, I wrote QGD when I meant QGA in my question. In the QGA after 1. d4 d5 2. c4 cxd4 both 3. e3 and 3. e4 have been played thousands of times, with 3. e4 being slightly preferred. So it is not clear to me why in the line from my questions 4. e3 is by far the most common move, while 4. e4 ends up in a QGA structure Commented Aug 17, 2023 at 10:01
  • @AlessandroCodenotti I extended my answer, lmk if you still have questions
    – wdk23
    Commented Aug 17, 2023 at 15:30
  • Great answer, thanks! Just a small typo: the e4 in "So, in order to actually regain the pawn white has to play e4 as not to overextend himself." should be an e3 instead! Commented Aug 17, 2023 at 17:08

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