Introducing the Petrosian QID
In this post, I will introduce the Petrosian Variation of the Queen's Indian, so that almost any player can understand the basic ideas of this opening. It arises after the following moves:
Why would White spend a tempo on a non-developing move like 4.a3 at such an early stage of the game? Well, let's say we start with the more natural 4.Nc3:
In this case, we've transposed to a Nimzo-QID Hybrid Variation (which could also have arisen via. 3.Nc3 Bb4 4.Nf3 b6), where White has a hard time achieving the e4 break. If White plays 5.Bg5 to renew the threat of e4, Black can cover the key square again with 5...Bb7, and then White would have to play a somewhat awkward move to cover the e4-square again. And even then, White may not be threatening the e4 push, as the following variation shows:
As we saw, Black can flick in ...h6/Bh4, so that e4 entails a pawn sacrifice after ...g5. Though White has good compensation in the final position above, Black could also have played 5...h6 6.Bh4 g5 7.Bg3 Ne4 8.Qc2 Bb7, avoiding the Nd2 idea and securing the e4-square as a post for his knight.
It should also be mentioned that playing a3 would indeed be wasteful, for after 1.d4 Nf6 2.c4 e6 3.a3?!, Black can switch to a Queen's Gambit Declined with 3...d5, where White's a3 move is not very useful:
a3 only makes sense after Black played ...b6!
However, before we explore this main line, I want to show a quite common positional opening trap at the club level:
Now let's return to the position after the correct 5...d5:
Here White has a wide choice of options, which may explain this variation's recent popularity. Normally Black would not be in a hurry to fianchetto his queen's bishop in the Queen's Gambit Declined complex, but at the same time, a3 is also not a developing move for White. The main line is 6.cxd5, which I'll cover here, but you may also like to explore 6.Bf4, 6.Qc2 and particularly 6.Bg5 Be7 7.Qa4!?, which aims to disrupt Black's normal setup, compared to the Tartakower QGD (1.d4 d5 2.c4 e6 3.Nc3 Nf6 4.Bg5 Be7 5.Nf3 h6 6.Bh4 0-0 7.e3 b6).
How would you assess the Carlsbad pawn structure arising after 6.cxd5 exd5? We can say White has a slightly improved version, because of the b7-bishop biting on granite (d5). I suggest switching to a Catalan setup in reply:
The position after 10.Bf4 feels slightly better for White, as Black will likely end up in a hanging pawns position after the dxc5/bxc5 exchange, and White's pieces are quite well placed to target the pawns with moves like Rc1, Qc2, Rfd1, and Ne5. The engine will claim that the position is equal, but that understates Black's practical challenges freeing his pieces from the task of defending his pawns.
After Black's correct recapture, 6...Nxd5, White again has a wide choice:
The main line is 7.Qc2, trying to support the e4 break in one go, but there are other options, with 7.e3 being the main alternative and 7.Bd2!?/7.Qa4 also being seen from time to time. For a recent win with 7.Qc2, you can access my analysis of Dreev-Bruzon for a $2 pledge to my Patreon site.
Here, I will cover 7.e3. Black has two ways to develop his king's bishop - to e7 or to g7.
Grunfeld's Spirit - 7...g6/...Bg7
Those of you who have Mega Database can access detailed annotations of the game by Stohl. I don't share these annotations here, because of copyright laws associated with making an analysis from a paid product available for free. However, I will explain the idea of 8.h4/9.h5 - White wants to make it difficult for Black to castle kingside, and thereby complete his development. In turn, compared to the Exchange Grunfeld (1.d4 Nf6 2.c4 g6 3.Nc3 d5 4.cxd5 Nxd5 5.e4 Nxc3 6.bxc3 Bg7), White has his pawn on e3, so his centre is more guarded from ...c5/...e5 thrusts, affording this flank play.
Having said all that...when we're assessing the merit of an idea, a key question to ask is 'what if we ignore the opponent's idea, or even deliberately 'fall into it' as Tal often liked to do? To be honest, even if Black 'castles into it' with 10...0-0 (instead of the game's 10...Nxc3), I can't prove a White advantage, for example:
The problem for White is that he can't get his queen to the h-file for the attack, as his pieces are in the way.
Black Develops Classically - 7...Be7
This continuation is likely to lead to the following position, after normal development by both sides:
This middlegame leads to a lot of decisive games, because of the unbalanced pawn structure. White is generally playing for a long-term attack on Black's king, using White's central space advantage, while Black plays to pressure White's center, arguing it is a target of attack. It's not always that simple though, as both sides have to constantly be watching for a liberating d5 break by White.
The following game is a good example of the kingside attack:
I know from personal experience that Sanikidze is quite strong with the White pieces, and he proves it again in another game from the Batumi Olympiad:
Time for a puzzle! What should White play in this position?
Now, the full game:
Tornike Sanikidze
To finish up, I should mention that Black can also try to be tricky with his move order, and play 4...Ba6 instead of the automatic 4...Bb7. In that case, the main line runs as follows:
The final position could be considered somewhere between equal and slightly better for White - White's center looks nice, but Black's pieces are all on natural squares and he has no weaknesses - a typical outcome for the Queen's Indian. But you may be wondering, why does Black play 4...Ba6 and then 5...Bb7? Is the queen really worse on c2 than on d1?
Answer: The idea is to play the ...c5 break, without allowing d5. Take the following moves as an example:
In this case, White achieved a decent version of a Modern Benoni structure, where Black's bishop is a bit unusually placed on a6. Granted, White can't play e4 without losing the right to castle kingside, but a recent Fedoseev game demonstrated that there are other appealing plans for White:
Thanks for your attention! Feel free to share your games in this variation in the comments below! 
