4.e3 is something I've referred to as the Slow Slav (4...Bf5 or 4...Bg4, while 4...e6 could transpose to a Semi-Slav). 
Useful post!
Do you have any up-to-date recommendations on the, Meran? As White, I'm especially concerned with this move order, e.g, 1 d4, d5; 2 c4, e6; 3 Nc3, c6; 4 Nf3, Nf6; 5 e3

fluffy wrote on 08/05/10 at 20:39:23:

Thx, fluffy, I fully agree with you and your replies #8 and #19 (the latter was your answer to a post of mine where I was slightly confused about sth. I'd like to explain.)

Today: 
I agree, today we refer to the Semi-Slav as everything that touches the position after 1. d4 d5 2. c4 c6 3. Nf3 Nf6 4. Nc3 e6 (or is classified by ECO-Codes D43-D49 which is just the same)

Historically (in the 20th century):
however, things were somewhat different, as chess theory mainly focused on the QDG and not the Slav. So quite a number of definitions were different from today. -- Euwe 1966 or BCO2 (Kasparow/Keene 1992) defined the Semi-Slav by the position that is reached after 
1. d4 d5 2. c4 e6 3. Nc3 c6

This has a number of consequences. For these 20th century authors, Noteboom or Marshall Gambit 4.e4 used to be discussed under the Semi-Slav lines! 

What is more, the name Moscow variation was used in 20th century (e.g. Taimanow 1980) for the line 
1. d4 d5 2. c4 e6 3. Nf3 Nf6 4. Bg5 h6 while today we take it for granted that Moscow variation means the position after 
1. d4 d5 2. c4 c6 3. Nf3 Nf6 4. Nc3 e6 5. Bg5 h6 6. Bxf6 (whereas 6.Bh4 is called the Anti Moscow line).

Summing up, all I want to point out is that there is historically quite some confusion about these definition. And off-hand I can't think of any other terretory of opening theory that has undergone a similar development and shift of focus and names.

Looking at these developments. Is anyone able to explain who was driving these changes (in the definition of the Semi-Slav) and when exactly this happened? I just gave samples from a few books I own and this does not allow me to make too precise conclusions, I'm afraid.

It's hard to believe this thread has gone on so long, but I thought I'd jump in with my own attempt at reconciliation (for the sake of Knightmare, mostly).

After 1.d4 d5 2.c4 c6, the opening is a Slav Defense.  From here, the game will turn into a Semi-Slav if: 

1) Black plays ...e6 before ...dxc4, or
2) Black eschews the chance to develop his LSB outside the pawn chain and plays ...e6 with the d-pawn still on d5.

Off the top of my head, that should clear things up and leave the Geller Gambit in the Slav proper.  Or did I just muddy the waters even more?

Note that I'm ignoring transpositions to the QGD, for instance, because they must go "through" the Semi-Slav and I name an opening variation based on the position reached, not the move order to get there.  Thus, 1.d4 d5 2.c4 c6 starts as a Slav, 3.Nf3 Nf6 4.Nc3 e6 changes to a Semi-Slav, and 5.Bg5 Nbd7 6.e3 finally transposes to a QGD.

H-HH wrote on 08/04/10 at 16:32:37:


Well, nice answer. Everything that refutes the definition is an exception, if I understand you. And around the Slav / Semi-Slav there are many.
But still the definition is correct? Extremely convincing, really.

The simple answer to the basic question what the definition of the Slav or the Semi-Slav (or basically any opening) is, is where the given position is listed in ECO. 
An example of the weaknesses of that System (and there are many) is the Geller-Gambit. Or the Vienna-Variation in the QGD to give another example. There simply is no "inner logic" in that System.

Anonymous3 wrote on 06/26/10 at 04:02:24:


Well, sorry, you both are wrong. Which is proven by the main line of the Geller-Gambit.

Though I like to add that trw is even wronger, as I do not think that there is a single line of the Semi-Slav with pawns on e6 and c6, where the bishop is outside the pawn chain. 

fluffy wrote on 06/29/10 at 13:27:05:


I couldn't disagree with any of these words.

If you have arrived at useful definitions, then just let me know what you think about this one: 1. d4 d5 2. c4 c6 3. Nf3 Nf6 4. Nc3 dxc4 5. a4 e6 *
A Slav or rather a Semi-Slav?

The situation isn't getting any easier when you look at the moves to come:

A) 6. e3 c5 7. Bxc4 Nc6 8. O-O cxd4 9. exd4 Be7 *
This looks very much like a QGA. However, the system of encyclopaedia of chess openings ECO stills classifies this as a Slav position (D16). The difference to a true QGA is minuscule. Here is pawn is on a7, while in the QGA after 1. d4 d5 2. c4 dxc4 3. Nf3 Nf6 4. e3 e6 5. Bxc4 c5 6. O-O a6 7. a4 Nc6 8. Nc3 cxd4 9. exd4 Be7 * Black has the pawn on a6.

B) 6. e4 Bb4 7. e5 Ne4 *
There are some famous Alekhine games vs. Euwe and vs. Bogoljubow with this line (and this move order). And yet this line gets an ECO classification of D31 (aka Semi-Slav) because the very same position can also arise from a Semi-Slav move order 1. d4 d5 2. c4 e6 3. Nc3 c6 4. Nf3 dxc4 5. a4 Bb4 6. e4 (?) Nf6 (?) 7. e5 Ne4 *
Some books or DVDs (e.g. Euwe 1966 or Shirov 2010) still preferred to discuss this line in their Slav sections. BTW, Euwe argues that in this Semi-Slav move order 6. e4 is weak because of the stronger reply 6... b5!

Tricky, isn't it?