Boi Variation

The Boi Variation, also known as the Classical Variation, answers 2. Bc4 with 2...Bc5, copying White's development. Black's bishop takes the a7–g1 diagonal and eyes f2, the counterpart of White's pressure on f7, while both of Black's knights and the f-pawn stay uncommitted. It is the third most popular reply to 2. Bc4, behind 2...Nf6 and 2...Nc6. The position remains symmetrical, and the drawback of that symmetry is that White, having the move, can strike first in the center with d4. Wikibooks considers the line less effective for Black for this reason, although the engine rates the position as close to level.

Much of the variation's practical weight comes from transpositions. The most frequent continuation, 3. Nf3, attacks e5, and after 3...Nc6 the game is a Giuoco Piano. 3. Nc3 heads for the Vienna Game. The quieter 3. d3 supports e4 and keeps several doors open: a later f4 can produce a King's Gambit Declined with Black's bishop already on c5, while Nf3 can lead to the slow maneuvering of the Giuoco Pianissimo.

In online play the second most common choice is 3. Qh5, which threatens mate on f7 and attacks the e5-pawn at the same time. Black can meet both threats, but White scores markedly better with this move in the Lichess database than with the developing alternatives.

White can also keep the game in independent Bishop's Opening territory. The Philidor Variation, 3. c3, prepares d4 to build a broad center and gain time against the bishop on c5; Black's sharpest answer is the Lewis Countergambit, 3...d5. The immediate 3. d4, the Lewis Gambit, offers the d-pawn to open lines and has produced good results for White. Other gambits are 3. b4, the McDonnell Gambit, which offers the b-pawn to deflect the bishop in the manner of the Evans Gambit, and 3. f4, the Stein Gambit, with a King's Gambit flavor. The Lopez Variation, 3. Qe2, is rarely seen.