Philidor Variation

The Philidor Variation is White's main independent answer to the Classical, or Boi, Variation of the Bishop's Opening. Rather than transposing with 3. Nf3 or 3. Nc3, White plays 3. c3 to support d4, which would hit the bishop on c5 and establish a broad pawn center. The drawback is that the queen's knight loses its natural square and d4 has not yet been played, so Black has a move to react in the center first.

The most common reply is 3...Nf6, with 3...d6 nearly as popular and 3...Nc6 well behind. After 3...Nf6 the critical line runs 4. d4 exd4 5. e5 d5 6. exf6 dxc4 7. Qh5 O-O 8. Qxc5 Re8+ 9. Ne2 d3 10. Be3, a forcing sequence of mutual captures in which Black's advanced d-pawn becomes a central factor. The immediate 3...d5, the Lewis Countergambit, is seldom played but is regarded as Black's most active option; it is named after the English player William Lewis, who published analysis of it in 1834. A further choice is 3...Qg5, the del Rio Variation, which attacks g2. Engines assess the position as balanced and favor ...d5, ...Nf6 and ...Qg5, while in online play White scores somewhat better.