exd5, freeing your bishop and you should be equal. It will essentially be a QGD exchange where white has put their knight on f3, which isnt the best square.
cxd5 would take you into a passive slav exchange, in which your LSB has no where to go (usually it comes out to f5 in the exchange slav).
While I am lower rated than the above poster, I want to clarify something that he has said because I think it is a little inaccurate.
It is not that Nf3 is necessarily not the best square, but that white should not commit to putting the knight on f3 just yet. Ideally, white would develop his queenside and LSB first and then decide where the knight goes. Ideally, white would play Qc2, e3, and Bd3 all before moving the g1-knight. This is mainly to limit the scope of the c8-bishop, because the d1-h5 diagonal is controlled (not blocked by an f3-knight) so it cannot go to g4, and with a queen on c2 or a bishop on d3, the f5 square will be unavailable. White wants to make sure that black cannot put that bishop anywhere useful, so he would try to clamp down on the f5 and g4 squares to stop black from developing it there. If white develops the f3 knight first, he might accidentally allow black the time to play ...c6 and ...Bf5 if he hasn't claimed the b1-h7 diagonal quickly enough. Also, there are some positions where the knight is wanted on e2 so white can play f3 and e4, but not always, and sometimes white can choose between several plans which may include the knight on f3 or e2 depending on what white wants to do.
I just think it's necessary to mention that the knight can be placed on f3 (Sammy Reshevsky played the exchange QGD with an eventual Nf3), just not right away because doing it right away can give black the chance to develop the LSB.
So what's this got to do with your question? Well, when white plays cxd5 and you play ...exd5, you have transposed into a QGD exchange where white has played Nf3 too early and has not claimed the necessary diagonals or developed his queenside with Bg5 and Qc2. Therefore, black can use this time to develop the LSB (sometimes by way of g6 and Bf5 if the queen is on c2) and get equality. This is why the move 5. cxd5 scores pretty poorly for white in databases, because it transposes into a version of the QGDE where white has played inaccurately.
Thanks guys, thats very helpful.
Also 5...cxd5 is playable, leads to an old fashioned slav exchange after 6Bf4 Nc6. Players like Lasker and Smyslov played it quite a bit. One plan is to use the bad bishop on the queen-side. Another to setup a stone-wall position with Ne4 and f5, as in a famous Capablanca v Lasker.
Club player's play c4xd5 a lot because it is safe and removes necessity of thinking about d5xc4. In the carlsbad structure after e6xd5, to begin to think about a white advantage, black's bad bishop needs to be restricted. Even then white is working with pretty small advantages.
Hi Guys, I've come across this playing black a few times at the 1350-1400 level. I'm not clear if the correct response is cxd5 or exd5 and why. Any guidance please? Thanks