Harmonist

The Harmonist, 1. e4 d6 2. f4, is a White reply to the Rat Defense that advances the f-pawn before the d-pawn. Instead of building the usual center with 2. d4, White claims e5 and kingside space at once. The d-pawn stays uncommitted. If Black later heads for a Pirc-type fianchetto, White already has the f4 pawn that defines the Austrian Attack. The cost is the usual one for an early f4: the king's position is loosened and the e1-h4 diagonal opens before White has developed anything.

Black's most common answer by a wide margin is 2...Nf6, chosen in over two-fifths of games. The knight attacks e4 immediately, so White has to spend a move defending the pawn before carrying on with the plan. Black keeps the option of ...g6 and ...Bg7, aiming the bishop along the long diagonal at the pawns White has advanced.

Two other replies are each played in roughly an eighth of games. 2...g6 starts the fianchetto without committing the king's knight, in the manner of the Modern Defense. If White adds d4 and Nc3, the game can reach structures familiar from the Austrian Attack. 2...e5 hits the f4 pawn straight away and contests the dark central squares that White's advance was meant to secure. Engine analysis also ranks 2...c5 among Black's best moves; it controls d4 before White has occupied it.

A more forcing option is the Fuller Gambit, 2...d5 3. exd5 Nf6. Black moves the d-pawn a second time and gives it up for quick development, betting that the early f4 has left White's position too loose to keep the extra material comfortably.

The engine rates the position after 2. f4 as level. In a large Lichess sample, White scores only marginally better than Black, and draws are unusually rare at around three percent, consistent with the unbalanced positions the early pawn advance tends to create. The Harmonist sits in the upper tier of named openings by frequency, though it is far less common than the transpositional main lines beginning with 2. d4.