There is a deep intellectual pleasure working in a medium as fantastically varied as chess. It is the joy of testing the strength of an idea, of one’s imagination.
The creators of chess art conquer the routine, and seek the unknown. — Bronstein
If Black accepts the pawn offer at f4, and White carries out his aim of d2-d4, then White gains small advantages in time (recapturing with a developing move) and space (deflecting Black from the center); and if Bc1xf4, White also neutralizes Black’s small advantage in material.
White typically faces three fundamental difficulties in executing this plan. We’ve talked about the first two; following 1. e4 e5 2. f4 exf4:
White’s first problem is ….Qd8-h4+; moves that prepare a useful interposition can be too tame;
Moves that precede fleeing from check can be too risky (and obstructive to oneself). White’s second problem is that the best compromise between piece activity and safety — the Bishop’s Gambit 3. Bc4 Qh4+ 4. Kf1 — can bury the king rook.
If White opts against interposition or flight, the third method for getting out of check is to capture the checking piece, giving us White’s most common third move: 3. Nf3. After 3. Nf3, Black’s most direct method of spoiling White’s plan of d2-d4 plus Bc1xf4 is to play 3…g5 to solidify the f4-pawn.
1.e4 e5 2.f4 exf4 3.Nf3 g5
White cannot easily play d2-d4 plus Bc1xf4, because that loses a bishop. As long as the f4-pawn stands, Bc1-e3 also loses the bishop. Meanwhile, Bc1-d2 is a lame development.
If the queen bishop rests, so does the queen rook. After White castles, the pawn at f4 also blocks the f1-rook.
Most pawns are worth about one pawn, but after 1.e4 e5 2.f4 exf4 3.Nf3 g5, I like to say that the obstructive value of the f4-pawn is roughly two rooks and a bishop.
The f4-pawn must fall for White to smoothly complete his development. I think that makes 4.h4 a positional necessity, but not everyone agrees. 4. Bc4 is equally popular, a good developing move that leaves the door open for Black to push 4…g4? without coercion (see Part 7: This Will Be on the Test).
That’s one of my most favorite games.
If Allgaier’s knight sacrifice doesn’t appeal, there’s Kieseritzky’s balanced 5.Ne5 — 1. e4 e5 2. f4 exf4 3. Nf3 g5 4. h4 g4 5. Ne5 —when Black has many reasonable moves. 5…Nf6 is probably the best of those; one of Morphy’s blindfold simultaneous exhibition opponents chose 5…d6 to jab the knight (TK pt. 2).