In the traditional queen's gambit, white offers their c pawn to the e5 pawn, threatening to take back with their f bishop and enjoying a central pawn advantage. My response is to play symmetrically, that way I can learn how to play it by defending against it first, so I reject the c pawn and offer my own pawn on c5 in response. I also like to place my knight on c6 after that.
A common opening theme is for a bishop to pin a knight and a royalty piece, inhabilitating the knight and threatening to double up a pawn thus weakening the castle pawns. My tipical response is to block with my bishop.
Is it possible to respond to both of these threats simultaneously in the same way that I respond to them individually? This is important because it would simplify my opening book significantly. The main challenge is that the f bishop is overloaded with the task of defending the thematic c pawn and the f knight.
Consider the following game:
1. d4 d5 2. c4 e6 3. Nf3 Nf6 4. Bg5 c5 5. e3
I would ideally delay c5, but I want to keep the example simple here. My dilemma is, how do I develop my f bishop? I can't move it to d6 because after:
1. d4 d5 2. c4 e6 3. Nf3 Nf6 4. Bg5 c5 5. e3 Bd6 6. dxc5 Bxc5
I would have wasted a turn moving my bishop twice in a row, and I would have to waste another one if I ever want to move my queen or protect against a Knight attacking my f6 knight.
I can't move my bishop to e7 either because after:
1. d4 d5 2. c4 e6 3. Nf3 Nf6 4. Bg5 c5 5. e3 Be7 6. Nc3 O-O 7. Bxf6 Bxf6 8. dxc5
And recapturing that pawn seems very awkward, all pieces are 2 moves away, and c5 is not a particularly good place for any piece to be, especially if cxd5 and the c file is open for white's a rook. At any rate the main theme of the opening is broken.
My best answer so far is to play b6, so that my c5 pawn will have 2 defenders. If after c5 my opponent immediately takes my pawn, I recapture with my bishop,
1. d4 d5 2. c4 e6 3. Nf3 Nf6 4. Bg5 c5 5. e3 b6 6. dxc5 Bxc5
However if I my bishop had already developed to its knight-guarding spot, I take with my b pawn.
1. d4 d5 2. c4 e6 3. Nf3 Nf6 4. Bg5 c5 5. e3 b6 6. Nc3 Be7 7. dxc5 bxc5