Why is it that the Van Geet Opening (Nc3) considered to be an unsound opening whereas the reti openi

i used to play Nc3 when i started out playing chess, but recently discovered that it is unsound as compared to Nf3, but didnt find a proper reason as to why it is so

Personally, I don't think that it is too bad but after e5 there isn't much of an advantage if there is any.

It isn't unsound... It just prevents the C pawn from moving which is quite valuable to white.  

just to compare :

In Reti, u usually use the moves Nf3-c4 with g3, playing in centre.

In Van Geet, if white plays Nc3-f4, u could expect some problems for white's king...

To sump up, Reti's idea is to give black centre to attack it with c4 or sometimes e4 : u can't do this in Van Geet opening so u give black more freedom and more chances to use centre.

But all this is abstract, chess is a concrete game and it is not so simple...

1. Nc3 (which I learned as the Mestrovic Opening) is perfectly sound.  After 1. ..e5, however, it's pretty much best to transpose into a Vienna (with 2. e4).  Basically, it lets you get to a Vienna without worrying about the possibility of your opponent playing the Sicilian Defense.  You might even call it an "Anti-Sicilian" system.  Even if your opponent does play 1. ..c5, you don't have to play into it, and a kingside fianchetto makes the c-pawn look somewhat overextended.

Also the Reti stops a pawn push (e5) and Nc3 doesn't (d4 still works)

computer likes van geet more than reti

Are the Veresov Attack and Vienna game considered good openings? Because after 1... e5 2. e4 transposes to the Vienna game, while 1... d5 2. d4 transposes to the Veresov, and 1... c5 2. e4 is a Closed Sicilian, which we know is OK. In fact, I'm trying to build a repertoire based on this.

Why can't white castle queenside? That's what I'd do. Then you can play f4. One example plan I thought about was something like fianchettoing your queenside bishop, maybe Nh3, planning f4 exf4 Nxf4, and Qf3, with several pieces pointing towards the Black kingside. Just a thought.

van geet has a funny name

Nc3 blocks the c-pawn while Nf3 blocks the f-pawn, the c pawn is arguably more important because it helps you fight for the center while not weakening your king, this is because of the starting placement of the king and queen in chess.

moving the c pawn opens up a diagonal to your queen, which can be beneficial (e.g. in the slav when after a premature Bf5? white can play Qb3, exploiting the diagonal opened by moving the c pawn). moving the f pawn opens up the diagonal to your king, which can be considerably weakening at least early on (such as in fools mate, where playing f4 g4 leads to Qh4# exploiting the open diagonal). moving the c pawn is therefore safer and more active early on, so blocking the f pawn is preferable to blocking the c pawn. this is why in most kings pawn openings as well white develops the knight to f3 first instead so that they can play something like c3 d4 later. when white develops the knight to c3 first (e.g. vienna) it often signifies that they want to attack the center using the f pawn, such as in the vienna gambit, but this isn't as popular likely because opening up a diagonal for your queen by moving the c pawn is preferable to weakening your king by moving the f pawn
van geet isn't really unsound but this is probably why its considered inferior

@10

Named after Dick van Geet

I do not know anyone who has considered 1.Nc3 as unsound. You can always transpose into regular opening territory. Its only independent value which can't be avoided is after black plays 1...d5, where I mean, after 2.d4 it's fine, and after 2.e4 d4 white's position may be slightly questionable, but black's position after 1.e4 Nc6 2.d4 e5 3.d5 Ne7 is workable, so playing it a tempo up can't be too bad either.

what? after 1.nc3 e5 you play 2.nf3! after which 2...nc6 3.d4 gets you independent lines which are better than a scotch (A certainly trappier)

FM Bruno Dieu is rated 2213.
1 Nc3 usually transposes.
1 Nc3 d5 is the most testing reply.

1 Nc3 d5 is most testing.
FM Bruno Dieu, what does you book recommend?
2 d4 transposes.
2 e4 d4 seems good for black.

He did not recommend it. He only said that " the manoeuvre Nb1-c3-b1 should not be considered a waste of time , since the black pawn is no better placed on d4 than on d7 "

1.Nc3 d5 2.e4 d4 3.Ne2 e5 4.Ng3

Van Geet about this position in his booklet (Van Geet opening, New In Chess, 1994)

"As there is nothing to fear from the black d-pawn anymore. White intends to play his bishop to c4, with prospects of a promising cooperation between this bishop and the g3 knight."

He gives a lot of analyses on all possible blacks 4th moves, too much to write it down here, but he is right. There is no reason to believe Black is better.

Here is a correspondence game with it

Cyrille Augereau is a great 1 Nc3 specialist, (Dunst, Van Geet, Knight on the left, Spleiner Eröffnung, Trojan Knight).