Czech Slav

After 1.d4 d5 2.c4 c6 3.Nf3 Nf6 4.Nc3, Black has a genuine choice about when, or whether, to take the c4 pawn. The Czech Slav commits early and with real intent to hold it: 4...dxc4, capturing before White can prevent it and before Black has developed any pieces at all. This is a very different decision from the ordinary Queen's Gambit Accepted, where the analogous capture happens on move two, before either side has built any real structure — here, both sides have already developed several pieces, which changes what 'holding the pawn' actually requires and what White can do to punish an attempt to keep it.

The prevention move that defines White's response

White's most natural way to win the pawn back would normally involve ...b5, defending it with a further pawn move — exactly the resource that makes the Slav's whole c4-grabbing plan viable in many similar structures. The Czech Slav specifically invites White's most testing response to that idea: 5.a4, ruling out ...b5 entirely and forcing Black to defend the extra pawn some other way or accept giving it back under less favorable circumstances. This single prophylactic pawn move is the whole reason the Czech Slav has its own body of theory distinct from other ways of meeting 4.Nc3 — everything that follows is a consequence of White taking away the most natural defensive resource before Black can use it.

How Black actually holds the pawn without ...b5

With ...b5 ruled out, Black turns to piece activity instead of pawn support: 5...Bf5, developing the light-squared bishop actively outside the pawn chain before ...e6 would otherwise block it, is the Czech Slav's signature follow-up. The point isn't only development for its own sake — an actively placed bishop supports the queenside pawn structure indirectly and gives Black real options for meeting White's eventual e4 or Ne5 central pushes, rather than passively waiting to see whether the c4 pawn can be held at all. Black's practical plan becomes less about defending one pawn forever and more about using the resulting piece activity to compensate if the pawn eventually has to be returned.

Why this differs from just accepting the Queen's Gambit outright

Both lines leave Black temporarily up the c4 pawn, which invites treating them as the same idea wearing two different move orders. They aren't. In the ordinary Queen's Gambit Accepted, Black hasn't played ...c6 at all, so the position is more open and the resulting structures are considerably different — often involving an isolated queen's pawn for White or symmetrical central pawns after further trades. The Czech Slav's structure, with ...c6 already played, keeps a more solid pawn skeleton throughout and leans on piece activity rather than open lines to generate counterplay, which makes the resulting middlegames noticeably different in character even though both start from the same basic 'take the pawn' decision.

Letting the bishop get trapped after all

The single most self-defeating error in this whole line is developing the bishop to f5 too slowly, so that ...e6 becomes necessary before it gets out — which traps it behind the pawn chain exactly the way a normal Queen's Gambit Declined would, throwing away the entire reason for choosing this move order in the first place. White has a matching failure of follow-through: playing a4 and then not backing it up with real queenside pressure, which lets Black's bishop development neutralize the whole point of the prevention move for free.

The main line once both sides finish developing

After 6...e6 7.e4, White finally reclaims the central space Black's early pawn grab conceded, and the position turns into a genuine fight over whether Black's active piece placement and the extra pawn (if it's still held) outweigh White's broader central presence. Black typically continues with ...Bb4, pinning the newly advanced e4 pawn's defender, or ...Nbd7 and ...Be7, preparing to castle and complete development before deciding whether the c4 pawn is worth defending any further into the middlegame.

For a different way of keeping options flexible on the same move, see the Chameleon Variation Slav. For the more open structure that results from taking the pawn before any Slav-style support structure is built, see the Queen's Gambit Accepted.