Yeah, I think I'm just going to default to QGD territory whenever I can't get a Nimzo that I want.
So you ask about 1.d4 Nf6 2.c4 e6 3.Nf3 d5 4.Nc3, and I'll just play 4...Bb4
When I played the QGD I got tired of the position after 4...Be7 5.Bf4 so the vienna / ragozin thing will be something fresh.
Why are you wanting to avoid 5.Bg5 in the Semi-Slav?
More theory.
If chess were my full time job, then sure, I'll play into every mainline in all my openings 
Just to be clear, objectively all normal semi slav lines are fine, played countless times by countless grandmasters.
If you wish to avoid theory in the 5.Bg5 line, I would highly recommend looking into the Cambridge Springs Variation, which follows 5...Nbd7 6.e3 Qa5. This is certainly a reduced amount of theory and can catch white players off guard if they are not familiar with the lines.
Thanks for the suggestion. I looked at it a bit, and it's fine, but I preferred the QGD lines I'm familiar with. It seems if white knows what he's doing the Cambridge springs can be a bit difficult for black.
Agreed. Another option could be to play the typical set-up with Be7, Nbd7, 0-0, b6 and Bb7 with the idea to push c5 which objectively leads to a small plus for white, however is playable. A sample line would be 1. d4 Nf6 2.c4 e6 3.Nf3 d5 4.Nc3 c6 5.Bg5 Be7 6.e3 Nbd7 7.Bd3 0-0 8.0-0 h6 9.Bh4 b6 and off the top of my head I believe 10.cxd5 should retain a slight advantage for white.
It is also possible to move back into Meran type positions in this line, by playing 9...bxc4 10.Bxc4 b5 11.Bd3 Bb7 in the line above and then playing for the c5 pawn push as in most Meran positions.
This might be something you are interested in as it cuts out a large portion of theory compared to the actual mainline of the Meran which occurs after 1.d4 Nf6 2.c4 e6 3.Nf3 d5 4.Nc3 c6 5.e3 Nbd7 6.Bd3 (6.Qc2 has also gained popularity recently) ...dxc4, which can lead to major complications where both players need to know their stuff.
And why not the Slav may I ask?
Sure, Slav is good. Maybe one day I'll play it. If for some reason I had to switch right now, I'd probably try the Slav first. I'm having fun with the Nimzo for now.
In those lines it's white's choice on move 5 though (Bg5 vs e3)
The difference in the 5.Bg5 Meran-type line compared to the mainline Meran is that the c1-bishop has developed outside the pawn chain, however this is not such a great deal and you are avoiding theory as you wanted to. Both lines lead to similar play.
How do you plan to play after 5.e3?
Yeah, like I said earlier, I'll play the vienna / ragozin stuff (Bg5 and ...Bb4)
Against 5.e3, I think like you were saying, I'd treat it like a better version of a tartakower QGD.
Not to counter all that good advice, but having played the Semi-Slav for some time I must say a good deal didn't make sense. You should probably consult some valid chess material on the subject.
Sounds like a plan.
As an advocate for the Semi-Slav, I might finally recommend you look into 1.d4 Nf6 2.c4 e6 3.Nf3 d5 4.Nc3 c6 5.Bg5 h6 (the Moscow Variation).
The point is that black aims for an improved Botvinnik because after 6.Bh4 dxc4 7.e4 can now be met with g5! White does have compensation for the pawn and play is quite interesting.
There is not that much theory for black here compared to Botvinnik or Meran lines which could be good for you, however you will have to put some time in learning the Moscow.
Of course 6.Bxf6 can be met with Qxf6 when black has equalised.
Not to counter all that good advice, but having played the Semi-Slav for some time I must say a good deal didn't make sense. You should probably consult some valid chess material on the subject.
Maybe they were trying to help me marry it to my current repertoire.
In the end it seems inviting semi slav position by transposition is not a reasonable choice (unless it was your main weapon at some point in the past). I should treat sidelines like sidelines and not double my work by transposing into the heart of a different theoretical line. That's the upshot for me from this toipc.
Sounds like a plan.
As an advocate for the Semi-Slav, I might finally recommend you look into 1.d4 Nf6 2.c4 e6 3.Nf3 d5 4.Nc3 c6 5.Bg5 h6 (the Moscow Variation).
The point is that black aims for an improved Botvinnik because after 6.Bh4 dxc4 7.e4 can now be met with g5! White does have compensation for the pawn and play is quite interesting.
There is not that much theory for black here compared to Botvinnik or Meran lines which could be good for you, however you will have to put some time in learning the Moscow.
Of course 6.Bxf6 can be met with Qxf6 when black has equalised.
Sure, I know this thing exists, but it would be ridiculous to learn the entire semi slav for the sake of a few move orders. If I wanted to play it I should just make it my main weapon and use QGD stuff for odds and ends.
To answer the op’s question about playing by principle, that is what I used to do and it worked fine for me up to uscf 1800+. Beyond that I ran into players that knew a little theory and played the harder lines to deal with.
To answer your question about playing by principle, that is what I used to do and it worked fine for me up to uscf 1800+. Beyond that I ran into players that new a little theory and played the harder lines to deal with.
Thanks for the feedback. IIRC no one answered that question directly.
It's a bit of a chess.com thing, the obsession with playing c6 and semi-slav, probably based on too much reliance on database stats. In the move order of your example, you could have just played Be7, and developed with castling, b6, Bb7, then c5, or 4...c5 immediately. So you can just play a straightforward Queens Gambit Declined with much less theory to worry about.
The move order I show is very deliberate. I have other things I play in other situations. So I am avoiding all the Bg5 semi-slav stuff. I was thinking I would just have to worry about the meran and anti-meran.
The move order you show cannot be forced. What about 1.d4 Nf6 2.c4 e6 3.Nf3 d5 4.Nc3!
NOW:
If you go Semi-Slav, you have to allow 5.Bg5
If you play 4...Bb4, you are no longer in a Semi-Slav or a Nimzo-Indian, but rather, a Ragozin, which is a line of the QGD (Not sure if it's D37, D38, or D39, or some combination of that).
You can reach it via the Nimzo with 4.Nf3 d5, but most don't transpose to the Ragozin after 4.Nf3 and prefer 4...b6 or 4...c5 with 4...O-O a distant third before 4...d5.