Question about the Semi-Slav

I noticed that there is a Semi-Slav tournament coming up and it says that all opening moves must be these:

All games start with the Semi-Slav,

1. d4 d5 2. c4 c6 3. Nc3 Nf6 4. Nf3 e6

http://www.chess.com/tournament/12th-chesscom-thematic-tournament---semi-slav-1401-1600

However the book opening says this:

Semi-Slav Defense (D43)

http://www.chess.com/opening/eco/D43_Semi_Slav_Defense

Also the chess website agrees with the book opening.

http://www.thechesswebsite.com/chess-openings/semi-slav.php

The opening that uses c6 instead of e6 is actually called the slav.

Slav Defense (D10)

http://www.chess.com/opening/eco/D10_Slav_Defense

http://www.thechesswebsite.com/chess-openings/slav-defense.php

So, it appears that there was a mistake and the name of the tournament should be changed to the Slav instead of the Semi Slav.

Something is weird. I investigated the semi slav after I saw the invitation for the tournament. I am an e4 player as white and play the Nimzo or Queens Indian as black against 1 d4 so I'm really not terribly familiar with the Slav or the Semi Slav as it isn't part of my arsenal.

However, I am noticing now that those differences exist in which opening is which.

I pulled out Modern Chess Openings 14th edition and it gives the following moves:

Semi-Slav: 1 d4 d5 2 c4 c6

Slav: 1 d4 d5 2 c4 c6

IM Silman's Complete Book of Chess Strategy agrees with it.

What is the difference? Why do these other sites claim that the Semi Slav is 1 d4 d5 2 c4 e6?

So is it that the chess website and the book opening recorded on chess.com are wrong?

Someone is wrong. 2...c6 and 2....e6 are very different moves. Which is the right one for the semi slav?

Semi-Slav is pretty much a mix between a Slav and QGD pawn structure to begin with. Notice in both your lines in the start end in exactly the same position? The only difference is in which order you move the pawns.

I think when you play c6 you leave yourself with the option to play either the Slav or Semi-Slav and when you play e6 you have the option to play a QGD or a Semi-Slav.

If Black plays ...c6 ...d5 ...e6 ...Nf6 in any order it is usually referred to as a Semi-Slav (although the QGD Cambridge Springs also has these moves).  In the Slav, Black refrains from playing ...e6 in the early going, and often develops his bishop ...Bf5.

Semi-Slav is part of the QG and Semi-Slav may arrive from the Slav.

Semi-Slav is charactreized by both ...e6 and ...c6 (forget about move order).

1.d4 d5 2.c4 (Queen's Gambit)

1.d4 d5 2.c4 c6 (Slav)

1.d4 d5 2.c4 c6 3.Nf3 e6 (This may become Semi-Slav or just QGD/Slav or even just English) 

1.d4 d5 2.c4 c6 3.Nc3 e6 (This may become Semi-Slav or just QGD/Slav or even Caro-Kann)  

1.d4 d5 2.c4 c6 3.Nf3 Nf6 4.Nc3 e6 (Semi-Slav from Slav)

1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.Nf3 c6 (Semi-Slav from its own, same position as above)

That makes sense. Thanks.

The best way to simplfy is no matter the number of moves if black puts in e6 it will probably transpose to the semi-slav,qgb ect.Thus the tournament moves were correct. Had e6 not been played it probably would have been a slav opening.

Although after c6 most people play KNF3 not KNC3. Both are good.

Alexey Dreev uses this move order :

1.d4 Nf6 2.c4 c6 in his book  The Meran & Anti-Meran Variations.

Those should all be slav move orders as d5 will be next for black. Although getting off track here the move order D4 KNF6 C4 C6 NC3 E6 NF3 BB4 is the Nimzo G3 or F3 lines

One important thing to consider is that opening variations are characterized first by pawn structure, and then by piece position, rather than by the actual move sequence leading to them.

the move to e6 will in most cases be a semi-slav move

The only way to play a true semi slav is by passing one move, and then playing c6 and e6 in one go. Both e6 and c6 will brush on the QG and the Slav, so this problem cannot be avoided.

I have one book that starts the semi slav with e6 and one with c6. So really it doesn't matter. Should white exchange in either case, it won't be the same opening. If white does not, the semi will be reached.

Part of the question of which move order to pursue comes down to whether you'd rather face the QGD exchange or the Slav exchange as black.  They have very different characters, and very different plusses and minuses.