user9924: I'm working on my positional play. Exclusively playing correspondence chess at the moment.
For white I play D4 and try for C4 after that.
For Black I play Caro Kann against E4 but am not sure what's most positional against D4.
I'm thinking of Slav, Semi Slav, QGD
For solid long term positional play which one is best investing time in learning in depth?

user9030: I recommend to play Stonewall Dutch, quite closed, yet quite active. 
[Event "Stonewall Dutch"]
[Site ""]
[Date ""]
[Round ""]
[White ""]
[Black ""]
[Result ""]
[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]

1. d4 f5 2. c4 Nf6 3. g3 e6 4. Bg2 Be7 5. Nf3 O-O 6. O-O d5 7. Nc3 c6  


user-1: The Caro-Kann and Slav share similarities, as discussed in the question: What are all the possible combinations of openings which work well together? (like the Slav+Caro-Kann combo). 
I play the 2 myself and find that the 2 openings appeal to players who:

Prefer endgames with a superior pawn structure, particularly playing against an isolated d-pawn or hanging c- and d- pawns
Don't mind exchanging the light square bishop, as in both openings this piece tends to be exchanged for a knight
Want a low maintenance repertoire, as the 2 have solid responses to 1. Nf3 and 1. c4
Have good defensive abilities, as both have a solid reputation. So, if you play against attacking maniacs or computers often then these 2 openings work well together


9924: <p>I'm working on my positional play. Exclusively playing correspondence chess at the moment.</p>

<p>For white I play D4 and try for C4 after that.</p>

<p>For Black I play Caro Kann against E4 but am not sure what's most positional against D4.</p>

<p>I'm thinking of Slav, Semi Slav, QGD</p>

<p>For solid long term positional play which one is best investing time in learning in depth?</p>
 9030: <p>I recommend to play Stonewall Dutch, quite closed, yet quite active. </p>

<pre><code>[Event "Stonewall Dutch"]
[Site ""]
[Date ""]
[Round ""]
[White ""]
[Black ""]
[Result ""]
[FEN "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"]

1. d4 f5 2. c4 Nf6 3. g3 e6 4. Bg2 Be7 5. Nf3 O-O 6. O-O d5 7. Nc3 c6  
</code></pre>
 -1: <p>The Caro-Kann and Slav share similarities, as discussed in the question: <a href="https://chess.stackexchange.com/questions/9546/what-are-all-the-possible-combinations-of-openings-which-work-well-together-li">What are all the possible combinations of openings which work well together? (like the Slav+Caro-Kann combo)</a>. </p>

<p>I play the 2 myself and find that the 2 openings appeal to players who:</p>

<ol>
<li>Prefer endgames with a superior pawn structure, particularly playing against an isolated d-pawn or hanging c- and d- pawns</li>
<li>Don't mind exchanging the light square bishop, as in both openings this piece tends to be exchanged for a knight</li>
<li>Want a low maintenance repertoire, as the 2 have solid responses to 1. Nf3 and 1. c4</li>
<li>Have good defensive abilities, as both have a solid reputation. So, if you play against attacking maniacs or computers often then these 2 openings work well together</li>
</ol>
