user8209: I really like to play openings that contain f4 (f5 as black) for a number of reasons.

It cannot be challenged with d pawn, which is initially protected by the queen.
When the king knight is developed, the f pawn is no longer blocked.
Unlike c pawn, it can be easily supported by castling kingside up to the board, and helps the development of the rook if exchanged.
After king's pishop fianchetto, the diagonal is open and the bishop is very strong there.
Even if exchanged early, after castling kingside, the king rook has a semi-open file, which makes it stronger.
Enables Ng5 move, which can be nasty sometimes.

But usually this move is considered bad, or dubious at the best by grandmasters and engines. What is the reason?


      [FEN ""]
      [StartPly "3"]

      1. e4 e5 2. d4 exd4 3. f4 Nc6 4. Nf3 Bc5 5. Bd3 Nf6 6. e5 Nd5 7. O-O O-O 8.
Kh1




      [FEN ""]
      [StartPly "3"]

      1. e4 e5 2. d4 d6 3. f4 exf4 4. Bxf4 Nf6 5. Nc3 Nc6 6. Nf3 Bg4 7. Be2




user19861: It depends on the position but in the second position you gave sf has white with a clear advantage. In the first position sf has it -.9 but black is up a pawn  which means the eval is based on black's material advantage. Positionally, white is a little better. I'm not sure where you're getting that white is worse positionally. 

user-1: This is not an answer regarding the general merits of f4 or ...f5, but a specific analysis of the first example:
  [FEN ""]
  [StartPly "13"]

  1. e4 e5 2. d4 exd4 3. f4 Nc6 4. Nf3 Bc5 5. Bd3 Nf6 6. e5 Nd5 7. O-O O-O (7...Ne3 {Forking Queen and Rook} 8. Bxe3 {Forced} dxe3 9. Be2 {One way to prevent ...e2+}) 8. Kh1 *

In the final position of the alternative variation, white is cramped, has lost the bishop pair and is passive due to the threat of ...e2+. I.e. playing f4 exposes the diagonal g1-a7 (and to a lesser extent the e1-h4 diagonal).
Your second example has a similar tactical weakness on the e1-h4 diagonal:
  [FEN ""]
  [StartPly "7"]

  1. e4 e5 2. d4 d6 3. f4 exf4 4. Bxf4 Nf6 (4...Qh4+ 5. Bg3 {Forced} Qxe4+ 6. Qe2 Nf6 {Black might as well develop a piece} 7. Nc3 Qxe2+ 8. Bxe2) 5. Nc3 Nc6 6. Nf3 Bg4 7. Be2


user12449: Firstly, #4 is wrong as the bishop is still blocked by the knight and, in your examples, the e pawn.  Change this to "adding support in the center."
There are two weaknesses with moving the f pawn early.  It weakens the kingside, especially the g1-a7 diagonal, and it wastes time in the opening.  These allow for a quick attack on your king.
However, looking over many King's Gambits, the advantages outweigh the disadvantages, and you should get many good games with your system.

user11629: It is not really possible to answer this generally as chess is more complicated and it really depends on what black is playing whether an early f4 is good or not.
I guess, what you actually like is the combination of e4 and f4. There are many examples where f4 is perfectly playable, such as in some Sicilians, the French defence and other semi-open games. 
In open games (1. e4 e5) playing an early f4 tends to be somewhat dubious at the highest level, but is of course perfectly playable at the club level.
If you want a system opening with f4, why don't you play the King's Indian Attack, where "f4" is often ok whatever black does?

8209: <p>I really like to play openings that contain f4 (f5 as black) for a number of reasons.</p>

<ol>
<li>It cannot be challenged with d pawn, which is initially protected by the queen.</li>
<li>When the king knight is developed, the f pawn is no longer blocked.</li>
<li>Unlike c pawn, it can be easily supported by castling kingside up to the board, and helps the development of the rook if exchanged.</li>
<li>After king's pishop fianchetto, the diagonal is open and the bishop is very strong there.</li>
<li>Even if exchanged early, after castling kingside, the king rook has a semi-open file, which makes it stronger.</li>
<li>Enables Ng5 move, which can be nasty sometimes.</li>
</ol>

<p>But usually this move is considered bad, or dubious at the best by grandmasters and engines. What is the reason?</p>

<pre>
<code>
      [FEN ""]
      [StartPly "3"]

      1. e4 e5 2. d4 exd4 3. f4 Nc6 4. Nf3 Bc5 5. Bd3 Nf6 6. e5 Nd5 7. O-O O-O 8.
Kh1
</code>
</pre>

<pre>
<code>
      [FEN ""]
      [StartPly "3"]

      1. e4 e5 2. d4 d6 3. f4 exf4 4. Bxf4 Nf6 5. Nc3 Nc6 6. Nf3 Bg4 7. Be2

</code>
</pre>
 19861: <p>It depends on the position but in the second position you gave sf has white with a clear advantage. In the first position sf has it -.9 but black is up a pawn  which means the eval is based on black's material advantage. Positionally, white is a little better. I'm not sure where you're getting that white is worse positionally. </p>
 -1: <p>This is not an answer regarding the general merits of f4 or ...f5, but a specific analysis of the first example:</p>

<pre><code>  [FEN ""]
  [StartPly "13"]

  1. e4 e5 2. d4 exd4 3. f4 Nc6 4. Nf3 Bc5 5. Bd3 Nf6 6. e5 Nd5 7. O-O O-O (7...Ne3 {Forking Queen and Rook} 8. Bxe3 {Forced} dxe3 9. Be2 {One way to prevent ...e2+}) 8. Kh1 *
</code></pre>

<p>In the final position of the alternative variation, white is cramped, has lost the bishop pair and is passive due to the threat of ...e2+. I.e. playing f4 exposes the diagonal g1-a7 (and to a lesser extent the e1-h4 diagonal).</p>

<p>Your second example has a similar tactical weakness on the e1-h4 diagonal:</p>

<pre><code>  [FEN ""]
  [StartPly "7"]

  1. e4 e5 2. d4 d6 3. f4 exf4 4. Bxf4 Nf6 (4...Qh4+ 5. Bg3 {Forced} Qxe4+ 6. Qe2 Nf6 {Black might as well develop a piece} 7. Nc3 Qxe2+ 8. Bxe2) 5. Nc3 Nc6 6. Nf3 Bg4 7. Be2
</code></pre>
 12449: <p>Firstly, #4 is wrong as the bishop is still blocked by the knight and, in your examples, the e pawn.  Change this to "adding support in the center."</p>

<p>There are two weaknesses with moving the f pawn early.  It weakens the kingside, especially the g1-a7 diagonal, and it wastes time in the opening.  These allow for a quick attack on your king.</p>

<p>However, looking over many King's Gambits, the advantages outweigh the disadvantages, and you should get many good games with your system.</p>
 11629: <p>It is not really possible to answer this generally as chess is more complicated and it really depends on what black is playing whether an early f4 is good or not.</p>

<p>I guess, what you actually like is the combination of e4 and f4. There are many examples where f4 is perfectly playable, such as in some Sicilians, the French defence and other semi-open games. </p>

<p>In open games (1. e4 e5) playing an early f4 tends to be somewhat dubious at the highest level, but is of course perfectly playable at the club level.</p>

<p>If you want a system opening with f4, why don't you play the King's Indian Attack, where "f4" is often ok whatever black does?</p>
