After 1.e4 c5 2.Nf3 e6 3.d4, why does White play and exchange the c5 pawn?
[Title "Why does White exchange the c5 pawn?"]
[FEN ""]
[StartPly "5"]
1.e4 c5 2.Nf3 e6 3.d4
If white does not do so, how can I take advantage of this?
As an example: 1.e4 c5 2.Bc4 e6 3.Bb3 Nc6 4.Nf3
what is the best response from black?
White doesn't always play d4.
Apart from the line you mention, there is also the King's Indian Attack and the Closed Sicilian, where white plays g3 and Bg2, the Grand Prix Attack, where white plays f4 and the Rossolimo, where white plays Bb5 (after Nc6 or d6).
In all those lines d3 is usually played instead of d4.
But 3.d4 is the most common line: It removes the influence of blacks c5-pawn on the centre and installs a knight on a very central square. This leads to a space advantage for white, which can often result in quick attacking victories. Black on the other hand has longterm trumps in his two central pawns and open c-file. This setup leads to strategically and tactically very rich positions, which explains part of the popularity.
Not playing 3.d4 doesn't lead to a worse position for white. It only arguably makes it easier for black to reach an equal position. Even the line you give, which really is unusual, doesn't guaranty black an advantage. He will probably just continue to develop with Nf6, Be7, 0-0 and maybe at one point expand on the queenside or play d5.
I recently have been pondering about Sicilian a lot! White plays d4 not because they want to bur because they have to. White will have to make bigger concessions if they want to avoid the loss of their d pawn to a wing pawn. First of all, if Nc3 appears and blocks c-pawn then without a d4, white will never have a claim in center. If B get outside and then we close with d3, mimicking an italian, then this B will be prone to attacks by a …d5 advance or later queenside expansions. If white’s LSB remains behind the pawn on d3 then white’s setup will not be at all threatening anything in opening. Surely, closed sicilian, Grand Prix attack, erc have their venom too but that comes in middlegame and often black has had time and freedom to develop and finnish their opening the way they want. So, as white youd rather give ip your d pawn and obtain active play for your pieces rather than assume a passive setup to avoid the contact on d4. If open sicilian was not good for white, then indeed 1…c5 would be a refutation of 1.e4.
There is though the question of how about white trying to play d4 by preparing with c3? That is indeed Alapin and one of my favorite. The truth is though that White is just not fast enough and there is not that Ruy Lopez type pressure on black’s position. Black has no pawn on e5 that is under constant pressure in Ruy Lopez. Basically black has no undefende pawn in center other than c5. It allows black to be the one who attacks white’s center first, either with mechanical …d5 or the positional …Nf6. Both of which are perfect choices for Black after 2…c3. However, Alapin leads to interesting middlegames and it is a game.
I too for the first time was shocked by white so easily giving up their central pawn. If left on my own, it would take me a thousand years to discover by myself that d4 was the right way for white! And no one explains this really. Do mot beleive then if they just pass it as an obvious move. It is not.
