(KW, June 3rd)
Let's stop a moment and think things through based on the current position
. Yes, e4 is weak, but can Black really take advantage of it at this point? Suppose on the next move Black moves Ne4 (This is an important step
, visualizing your opponent's next couple of moves). Can he keep it there? No! As you point out, d3 will force the Knight to move (as well, by making a developing move at the same time as forcing a piece away, White would gain at least one tempo and would seize the initiative by waiting for Black to make this move - an important consideration in the opening).
But where would the Knight move? It can't move to c5, d6 is a ridiculous move jumbling up his pieces (think piece coordination), possibly g5, but since the pawn move d3 opens the Bishop, White would take the Knight with no compensation. OK. So how about attacking c3? Would be taken immediately by Nxc3. Nxf2 then? No. White would simply retake with the Rook winning Knight for pawn, and it creates a half open file for White without any compensation, other than a slightly weaker castled King. I would still like that position as White. No. It would have to move back to f6 without creating any weaknesses in White's position, but in fact helps White's development. The Knight is not going to move there (e4), and so I need to concentrate on other squares where a move may be advantageous.
OK, how about d4? It is attacked once, and d5-d4 is not really an option for Black at this point, as it goes against his last move (e6) and screws up his pawn structure (Backward Pawn
My side is safe enough. Back to general strategic considerations, and consider how to attack the center, now on Black's side of the board.
By his last move, Black is creating a Weak Square Complex
(he has 5 pawns on light squares, and has locked in his light square Bishop) on the dark squares. Right now, the Nf3 is observing e5 and controlling that square (e5 is vulnerable
for Black), and does not want to move now, knowing that any pawn or piece that occupies a square no longer controls the square
White could easily be ousted by Nc6. So if White really wanted that Knight to go to e5, he could now play c3 following it up with d4, forming a chain and a base for the outpost on e5 (similar to the c3 Sicilian, from which this position could arise). Black would undoubtedly either attack the d4 pawn, or advance the c pawn to c4, locking in the pawn structure, constricting White's Queenside, and preparing for a later attack to the base of the pawn chain (either plan is used in the French defense).
The other major plan, as mentioned above, is to isolate the pawn on d5. This would open the diagonal for Black's Queen Bishop, but it would force Black to the defense of this pawn. The choice is now up to White how he wants to proceed.