Why is the Dutch defense (1.d4 f5) concidered a reliable defense , while the Bird-opening (1.f4 d5) is not ?

Why is the English opening (1.c4 e5) not superior to the Sicilian (1.e4 c5) ?

You are playing with an extra tempo,but still it is not possible to refute these defenses ?

There's another thing that separates the "reverse" opening, not just the tempo, but the fact that black need not play the corresponding moves.   So yes, in theory, 1.  f5, d5 is a Dutch defense in reverse, there is absolutely no compelling reason for black to accept this scenario.   He can play any number of other moves/systems, specifically aiming at a systematic dismantling or simply at a positional advantage.   

Same goes for playing Sicilian in reverse.   Yes, the positions SHOULD favor white if he is in fact playing Sicilian Defense with a move in hand, but this is not necessarily the case.   

So it is omission that does the trick ?

After 1.f4 e5 white can choose for either 2.fe5 d6 (From gambit) or 2.e4 ef4 (Kings gambit) .But after 1.d4 f5 2.e4 fe4 white lacks the ability to play 3.d3  so there's no reversed From-gambit.

That's a good example, yeah.   So all of a sudden the positions that a guy was hoping for maybe don't show up, and it's up to the individual player to decide whether the intentions of opening in reverse are meeting up with his strategic desires or not.   Bird's opening isn't "wrong" or "bad", neither is 1.c4, but you have to be able to play them whichever way your opponent decides.   If you are a fantastic Dutch Defense player and you feel very comfortable with your f-pawn out, your queen presumably on dark squares, and a fairly aggressive kingside formation... then by all means, play the Bird and kick some ass.   I have certainly known guys who did so.  

Remember that Savielly Tartakover said something to the effect of "If an opening's reputation is bad enough, it must be playable."

Thanks for taking the efforts to explain.By the way , how did you manage to add the (very nice) Tartakower game ?

An introduction to The Polar Bear System #1

http://www.youtube.com/watch?v=OFfQASWu-Bk

An introduction to The Polar Bear System #2

http://www.youtube.com/watch?v=RoOHRP44ub4

GM Henrik Danielsen has made several youtube videos on the f4 line.   They are worth watching, in my opinion.

IF you click the chessboard icon top left of the typing box, it will allow you to put in a static position or a series of moves.   That's all there is to it.  Game should say 1936 not 63

Why would you give away all your advantage as white by playing 1. f4? 
After 1. c4 black doesn't have to play 1..e5.

It is not my intention to play 1.f4 because ,like you, I don't consider it to be a good opening. I was more interested in the extra tempo White has in comparison with the Dutch defence.

Same counts for 1.c4 when Black actually chooses 1. .. e5 . It then becomes a Sicilian with an extra tempo.

FirebrandX and Unmaster both give strong arguments in that they state that Black is not obliged to play a reversal. I think I'm getting it ...

Give it a few more months, and their ideas just might sink in.  One hopes.

In the From Gambit white can play:

Sometimes an extra tempo isn't helpful.

@Definitely :

Thanks for the diagram. I already mentioned this possibility in #3

Ain't that the truth.....

Sometimes an extra tempo is detrimental.  As in the case of those who want to play 1.f4.  I've been fascinated by the Dutch defense for many years, so like pell13, I've wondered why the "Dutch a tempo up" (Bird's opening) isn't considered a good opening for white.  It often gave me poor results when I experimented with it years ago.  Broadcasting on move 1 the intention to play this system apparently gives the opponent sufficient compenstaion for white moving first.  Even from the black side of the Dutch, it is often best to transpose into the Dutch by postponing ...f5 by a move or more.  One could argue that the intitial chess board position is zugzwang for those who want to play 1.f4  

There is a reverse From's Gambit. 1. e3 f4 2. e4.