Why did he did so?

[Barry Sandercock]

I don't think it is a bad move. It depends how he follows it up.

[soheil_hooshdaran]

The author said it was

[IM Jack Rudd]

I don't like the look of f5 because black will respond with ...e5, and he has a solid line of protected passed pawns in the centre. If you leave the pawn on f4, black's d4 pawn is much more vulnerable to attack.

[Richard Bates]

The author said it was

Does this author ever deign to explain himself?

[Kevin Thurlow]

"Does this author ever deign to explain himself?"

Perhaps the author thought it was obvious!

I'm not saying that's the right approach, but some do it...

[MartinCarpenter]

Ah. Having consulted Stockfish there are some concrete drawbacks.

I was - and maybe the author too? - thinking about d3 in response. That does win an exchange via Bf2 but leaves white much better. However after the disgusting, inhuman response to f5 of exf5 white can't go Nxf5 as d3 is then really quite strong.

In fact its rather inconvenient for white to get organised. Probably enough so that its better to do something else to start with.

[soheil_hooshdaran]

Why would White want to play f2-f4 in:
r1bqkbnr/1pp3pp/p1p2p2/4p3/4P3/2N2N2/PPPP1PPP/R1BQK2R w KQkq - 0 6

[IM Jack Rudd]

Because it gives black the unenviable choice between (a) letting white play fxe5 and responding with fxe5, leaving him with a weak pawn on e5, or (b) letting white play fxe5 and responding with {piece}xe5, or playing exf4 himself, leaving white with control of the centre.

[soheil_hooshdaran]

Wouldn't White's pawn structure be compromised in case of b, then?

[IM Jack Rudd]

White's pawn structure is fine. What would be wrong with it?

[soheil_hooshdaran]

He would have 3 pawn islands then, and e4-pawn would be isolated

[Richard Bates]

He would have 3 pawn islands then, and e4-pawn would be isolated

It is not often one comes across a literal, rather than metaphorical, example of somebody actually arguing that black is white.

[soheil_hooshdaran]

He would have 3 pawn islands then, and e4-pawn would be isolated

It is not often one comes across a literal, rather than metaphorical, example of somebody actually arguing that black is white.

I am not arguing so.

[John McKenna]

You may think you are "not arguing so", however, because, from your own example position, you are confusing a resulting Black pawn structure - with three pawn islands and an isolated pawn on e5 - with a non-existant White pawn structure, you are indeed literally "arguing that black is white" and against yourself, due to a kind of chessical mental mirage in which your mind's eye is seeing a real Black pawn structure reflected onto an unreal White one. It is a just a trick of the light, and the dark.

Imagine that it is White to move in the position you gave, but with all the major and minor pieces removed from the board and with the White K on the square e3 and the Black K on the square e6, then after 1.f4 exf4 2.Kxf4 White has only two pawn islands, not three, and White's pawn on e4 is not isolated because there is a white pawn on d2. That is the opposite of what you argued.

[soheil_hooshdaran]

Oh, forgot about d2