I think it’s not just that 5 Nf3 transposes to main lines; it actually restricts White’s choices quite unhelpfully. For a start, Black could now continue 5…dxe5 6 Nxe5 g6 with a Kengis System (4 Nf3 dxd5 5 Nxe5 g6) where White has chosen 6 c4. This is playable, of course, but most wouldn’t consider it the critical test of the Kengis: Black’s coming ..Bg7 and …c5 annoyingly undermines the e5 knight.

Perhaps more serious, Black can simply play 5…g6. This is an Alburt system where White has chosen 5. c4, a move which is not often played. If White continues 6 exd6 cxd6 then he is back in an Exchange variation where he has cut out his trendy option of the Voronezh line (5 exd6 cxd6 6 Nc3 g6 7 Be3 Bg7 8 Rc1 00 9 b3), although to be fair he has conned Black out of the ….exd6 variation (which wouldn’t go with …g6)

So maybe 6. Be2 but now 6…. dxe5 leads either after 7. Nxe5 to the 6 c4 Kengis
where White has further limited his choices by the non-critical 7. Be2, or after 7.dxe5 Qxd1+ to White being forced to move his king (else the c-pawn hangs).

So I guess 6.Nc3 Bg7: White can still get back to the Exchange variation but otherwise he’s a little stuck: 7. Be2 dxe5 is still annoying so maybe 7. Be3 00 8. Be2 Nc6; now White has to exchange on d6, I think, and again it’s a ..cxd6 Exchange variation with White having committed to a variation not really considered critical.

Obviously 5. Nf3 is not exactly going to lose by force, but I think it has no advantages over either 4 Nf3 or the Exchange, and a few disadvantages.

Greetings,

  Is it possible that White should delay Nf3 in order to prevent the pin with ...Bg4?  I recall that the Voronezh variation in the Alekhine Exchange delays the development of the king's knight.

Your Humble Servant,

Bilbo

A Texan normally stranded in New Jersey, but back home for the holidays.

I think the main reason why 5.Nf3 doesn't get mentioned more is that it is likely to transpose into one of the main lines, so there are very few independent possibilities.

Ben Hague