thanks any reccomended lines?
What to do after 1.d4 d5 2. c4 c6 3. Nc3 Nf6 4. Bg5

It's all about move order. This is why 3.Nc3 is often answered with 3...dxc4, whereas 3.Nf3 is answered by 3...Nf6 4.Nc3 dxc4.
After 3.Nf3 Nf6 4.Bg5, the answer is simple, 4...Ne4 and already Black's at worst equal.
But against 3.Nc3, the Knight trade, while it does place a pawn in White's camp and might make it slightly more difficult to develop, it also leaves Black with a long term endgame weakness.
It's all about move order. This is why 3.Nc3 is often answered with 3...dxc4, whereas 3.Nf3 is answered by 3...Nf6 4.Nc3 dxc4.
After 3.Nf3 Nf6 4.Bg5, the answer is simple, 4...Ne4 and already Black's at worst equal.
But against 3.Nc3, the Knight trade, while it does place a pawn in White's camp and might make it slightly more difficult to develop, it also leaves Black with a long term endgame weakness.
First of all, Im sorry if I am wrong. But if 4...Ne4, what about the queen?

It's all about move order. This is why 3.Nc3 is often answered with 3...dxc4, whereas 3.Nf3 is answered by 3...Nf6 4.Nc3 dxc4.
After 3.Nf3 Nf6 4.Bg5, the answer is simple, 4...Ne4 and already Black's at worst equal.
But against 3.Nc3, the Knight trade, while it does place a pawn in White's camp and might make it slightly more difficult to develop, it also leaves Black with a long term endgame weakness.
First of all, Im sorry if I am wrong. But if 4...Ne4, what about the queen?
What about the Queen? She sits safely on d8.
Read the subject line. This is the SLAV, NOT THE ORTHODOX!
1.d4 d5 2.c4 c6 (NOT e6) 3.Nc3 Nf6 and now 4.Bg5 is not a particularly good move because the Knight is free to move.
Black's e-pawn is still on its original square!

First of all, Im sorry if I am wrong. But if 4...Ne4, what about the queen?
Which queen?
Anyway, 3.Nc3 Nf6 (3...dc4 also goes, but 3...Nf6 is more principled) 4.Bg5 dc4! 5.a4 (else Black protects the c4 pawn without having to worry about his non-pinned knight at f6) Qa5 6.Nf3 (6. Bd2 e5!) Bg4!? or 6...Ne4 7.Bd2 Nxd2 8.Nxd2 e5 9.Nxc4 Qb4, and Black is doing fine.
Or 3.Nf3 Nf6 4.Bg5 Ne4, as already mentioned.
I have reached this position in a number of my tournament games. I know that e6 is possible transposing into the semi-slav, but i am mainly a slav player so in the past i have played dxc4. After 4...dxc4 the most common line is 5. a4 Qa5. Why are these the most common moves? What experience do you guys have with this position? Could anyone post some lines that they play?
Thanks so much, Elias