Slav defence ia an attempt to resolve Black's traditional issues
in the Queen's Gambit Declined: the light Bishop development (usually
blocked by the pawn on e6), the pinning of the f6 Knight, the
possibility for White to launch a minority attack on the Queen's side (prepared by the change
the Slav defence these disadvantages disappear: the Bishop in c8 is not
locked, the pinning with Bg5 is not possible because the Black pawn is
still in e7 and after the cxd5 cxd5 the pawn
structure remains symmetrical. Furthermore, if Black takes the
pawn on c4, he is able to defend it with b7-b5, that is
possible as the c6 pawn defends the b5 square. The drawback
is that the thematic pawn break in c5 costs two moves instead of one.
Besides the light Bishop development is not so easy due to the weakness
that it leaves over the b7 pawn.
The Slav Defence is solid and can generate complex
positions, suitable for those wanting to play for a win also with