In the following Benoni position (White to move):

rnbqkbnr/pp3ppp/3p4/2pPp3/8/2N5/PPP1PPPP/R1BQKBNR w KQkq e6 0 4

The engine's (Lichess' Stockfish) first move, and also the one with best results (although very few games) in Lichess, is 4.a4. What's the purpose of that move? I can understand playing a4 when Black plays ...a6, to prevent b5, or when White has played Bb5 and Black replies ...Bd7, but playing 4.a4 seems premature to me.

  • 4.a4 is there to overprotect b5 in order to free the knight on c3, which itself aims at the c4 push. If say 4.Ne4 with the idea of c4 next, Black has the immediate 4...b5.
    – Pit
    Jan 11 at 19:07
  • @antonro: 1st choice by which margin? I ran LiChess Stockfish and "best move" is Nf3, but the difference to a4 and e4 (the obvious choice) is around 0.2. And this wildly fluctuates with depth, at the moment a4 is in front again... Jan 12 at 9:24

1 Answer 1


White is pretty sure they'll have to play a4 at some point, while the rest of the pieces don't have a certain square yet.

The statistics don't mean too much by themselves as we need to take transpositions into account. For instance, White could go 4.Nf3 now (the g1 knight will most certainly go for Nf3-Nd2-Nc4) and play a4 soon after reaching the same positions.

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