user1816: I am a keen player of d4 as white. One of the things that I often read is that the exchange variation of the Queens Gambit Declined is generally considered good for white:
[fen ""]
1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. cxd5 exd5

But the exchange variation of the Slav (or exchanging after Nc3 in the Slav) is considered better for black:
[fen ""]
1. d4 d5 2. c4 c6 3.cxd5 (3. Nc3 Nf6 4. cxd5 cxd5) 3...cxd5

I checked http://www.chessgames.com/perl/explorer and it seems to support this view, with the following win/draw/lose statistics for white for the above variations:

QGD All Variations: (41%, 37.7%,21.3%)
QGD Exchange:  (49.8%,35.3%,14.9%)
Slav All Variations: (37.8%, 41.3%, 20.9%) 
Slav (early exchange): (22.5%,55.2%,22.3%)
Slav (exchange after Nc3): (30.2%,49.9%,19.9%)

So it seems clear that the exchange of central pawns favours white in the QGD, but favours black in the Slav.
My question is simply - why? The resulting positions are superfluously similar (in the Slav black is missing the c-pawn, while in the QGD the e-pawn), yet positionally these must be very different! Is there a simple explanation of why this is the case? Would a clever newbie (i.e. somebody who plays chess very well, but have never played these variations) be able to make this deduction over the board through pure reasoning, or is this the type of thing you can only deduce by studying the opening theory?

user1811: The exchange variation in the classical QGD can be viewed as theoretically favouring white because after the fourth move in your game, white has both his central pawns while black has only one. However, black now has a semi-open central file which he can use to control the centre through his rooks. Also, he has a queen side pawn majority and he can start pushing his pawns forward on the queen side and try and gain an advantage. So, if black is clever, he can hold his own. 
By contrast, the exchange in slav yields a symmetrical position and also allows black to develop his Q Knight to its natural square,so black can be said to have achieved equality, which is definitely a good thing in a queen's pawn game.

user1856: The Principle of Two Weaknesses is at work here, one weakness is easier to defend than two.
Asymmetry, especially in pawn structure, benefits the player ahead in development, because there is usually available play on more parts of the board. The situation becomes more of a race, and the faster developed player will have an easier way to obtain an advantage.
Symmetry on the other hand, usually leads to play on one same section of the board. In the case of the Exchange Slav, play will most often revolve around Queenside (or otherwise someone has to break the symmetry by playing e4 or ...e5 leading to isolated queen pawn position, at the cost of weakening their own pawn structure).
Simply put, asymmetry often creates potential for two weaknesses, symmetry often creates only one, which is easier to defend against. As white you have the advantage of the first move, so it is wiser to aim for asymmetrical structure if you want any sort of advantage out of the opening.

user1485: Short answer: In symmetric positions it's difficult to get an advantage if there's nothing concrete. In the Exchange Slav white only has an extra half-move against black's very solid position. Compare with the Exchange French which is even more drawish.
In the Exchange variation of Queen's Gambit Declined on the other hand, there is a structural imbalance that white can try to exploit. The white position is quite flexible, there are many different strategies to choose from that lead to complicated play. White can go for the minority attack (b4-b5), play in the center (f3 followed by e4), and there are other options depending on the concrete line. In most lines white has a small, but real, advantage.

user291: White happens to have a couple of nice concrete plans in the particular QGD Exchange variation you mention (1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.cxd5 exd5). One involves e3, f3, Nge2, and a break in the center with e4. The other is a minority attack on Black's a7-b7-c6-d5 pawn structure with b2-b4-b5. You will note that White's stats are much worse in the variation 1.d4 d5 2.c4 e6 3.Nf3 Nf6 4.cxd5 exd5, even though the pawn structures are the same, because he no longer has the f3/e4 plan. So it is not nearly as simple as "the exchange of pawns favors White in the QGD but favors Black in the Slav."

1816: <p>I am a keen player of d4 as white. One of the things that I often read is that the exchange variation of the Queens Gambit Declined is generally considered good for white:</p>

<pre><code>[fen ""]
1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. cxd5 exd5
</code></pre>

<p>But the exchange variation of the Slav (or exchanging after Nc3 in the Slav) is considered better for black:</p>

<pre><code>[fen ""]
1. d4 d5 2. c4 c6 3.cxd5 (3. Nc3 Nf6 4. cxd5 cxd5) 3...cxd5
</code></pre>

<p>I checked <a href="http://www.chessgames.com/perl/explorer" rel="nofollow">http://www.chessgames.com/perl/explorer</a> and it seems to support this view, with the following win/draw/lose statistics for white for the above variations:</p>

<ul>
<li>QGD All Variations: (41%, 37.7%,21.3%)</li>
<li>QGD Exchange:  (49.8%,35.3%,14.9%)</li>
<li>Slav All Variations: (37.8%, 41.3%, 20.9%) </li>
<li>Slav (early exchange): (22.5%,55.2%,22.3%)</li>
<li>Slav (exchange after Nc3): (30.2%,49.9%,19.9%)</li>
</ul>

<p>So it seems clear that the exchange of central pawns favours white in the QGD, but favours black in the Slav.</p>

<p>My question is simply - why? The resulting positions are superfluously similar (in the Slav black is missing the c-pawn, while in the QGD the e-pawn), yet positionally these must be very different! Is there a simple explanation of why this is the case? Would a clever newbie (i.e. somebody who plays chess very well, but have never played these variations) be able to make this deduction over the board through pure reasoning, or is this the type of thing you can only deduce by studying the opening theory?</p>
 1811: <p>The exchange variation in the classical QGD can be viewed as theoretically favouring white because after the fourth move in your game, white has both his central pawns while black has only one. However, black now has a semi-open central file which he can use to control the centre through his rooks. Also, he has a queen side pawn majority and he can start pushing his pawns forward on the queen side and try and gain an advantage. So, if black is clever, he can hold his own. </p>

<p>By contrast, the exchange in slav yields a symmetrical position and also allows black to develop his Q Knight to its natural square,so black can be said to have achieved equality, which is definitely a good thing in a queen's pawn game.</p>
 1856: <p>The Principle of Two Weaknesses is at work here, one weakness is easier to defend than two.</p>

<p>Asymmetry, especially in pawn structure, benefits the player ahead in development, because there is usually available play on more parts of the board. The situation becomes more of a race, and the faster developed player will have an easier way to obtain an advantage.</p>

<p>Symmetry on the other hand, usually leads to play on one same section of the board. In the case of the Exchange Slav, play will most often revolve around Queenside (or otherwise someone has to break the symmetry by playing e4 or ...e5 leading to isolated queen pawn position, at the cost of weakening their own pawn structure).</p>

<p>Simply put, asymmetry often creates potential for two weaknesses, symmetry often creates only one, which is easier to defend against. As white you have the advantage of the first move, so it is wiser to aim for asymmetrical structure if you want any sort of advantage out of the opening.</p>
 1485: <p>Short answer: In symmetric positions it's difficult to get an advantage if there's nothing concrete. In the Exchange Slav white only has an extra half-move against black's very solid position. Compare with the Exchange French which is even more drawish.</p>

<p>In the Exchange variation of Queen's Gambit Declined on the other hand, there is a structural imbalance that white can try to exploit. The white position is quite flexible, there are many different strategies to choose from that lead to complicated play. White can go for the minority attack (<code>b4-b5</code>), play in the center (<code>f3</code> followed by <code>e4</code>), and there are other options depending on the concrete line. In most lines white has a small, but real, advantage.</p>
 291: <p>White happens to have a couple of nice concrete plans in the particular QGD Exchange variation you mention (1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.cxd5 exd5). One involves e3, f3, Nge2, and a break in the center with e4. The other is a minority attack on Black's a7-b7-c6-d5 pawn structure with b2-b4-b5. You will note that White's stats are much worse in the variation 1.d4 d5 2.c4 e6 3.Nf3 Nf6 4.cxd5 exd5, even though the pawn structures are the same, because he no longer has the f3/e4 plan. So it is not nearly as simple as "the exchange of pawns favors White in the QGD but favors Black in the Slav."</p>
