Chess Opening Theory/1. d4/1...d5/2. c4/2...e6/3. Nf3

= Queen's Gambit Declined = With 3.Nf3, White begins the development of his minor pieces after establishing a pawn center on the first two moves. 3.Nf3 controls important central squares, but unlike 3.Nc3, it does not immediately help to prepare the e4 pawn break. However, it does bring White close to castling kingside, something 3.Nc3 does not. In most QGD lines, White will play both Nc3 and Nf3 anyway; the order is important only if White desires to avoid specific variations.

White's dark-squared bishop will likely go to g5 after Black plays Nf6, but of course this is not possible immediately because of 3...Qxg5. Moving the bishop to a different square on move 3 would simply lose a tempo if it later went on to g5, so it is best to develop a knight here instead. There are sound systems involving Bf4, but it is not wise to commit to a Bf4 system so early. Thus 3.Nc3 and 3.Nf3 are the most sensible options.

Theory table
.

'''1. d4 d5 2. c4 e6 3. Nf3'''