Which openings do my opponents play?

The answer which I gave at a reaction upon my previous article (see Dutch version of this blog) wasn't complete.  I wrote that the number of openings even with a very narrow repertoire is gigantic. But gigantic is something intangible. Can't we define a more concrete number? Well I'll give it a try with this article.

However before we start the number-crunching, we should first agree about the definition of what is an opening. I consulted multiple sources and discovered there exists no consensus about this. The summary by ECO (Encyclopedia of chess openings) is the only standard existing today but the system only categorizes the openings in 5 main-categories and 500 sub-categories. So ECO classifies openings but doesn't tell us what exactly is an opening or how many moves counts an opening.

In fact it doesn't really matter for this article as we are only interested in how far somebody can be booked up. In other words how many moves can a player memorize of an opening. Of course this depends of the player and the opening itself. I know quite some lines beyond move 20 see e.g. mistakes and copycats. Beginners often don't know more than just a couple of moves. World-class-players on the other hand sometimes know lines as deep as move 40. Still a high rating is not a guarantee of knowing much about an opening see surprises part 1. In short we don't know what players know or don't know and that is only intensified by many players consciously hiding their opening-knowledge see secret.

So I am obliged to arbitrarily draw a line for the opening. As reference I use the default settings to create an openingbook in Chessbase. On my blog I showed countless examples of my openingbook see green moves, to analyze using a computer part 3, studying openings part 2, using databases, ... but nowhere I explained which settings I used to create that book.

Default (standard) 20 moves are used with a deviation linked to ECO. This means we use averagely 20 moves for an opening-line. More moves are used for lines in openings defined by ECO as popular while less moves are used for lines in openings defined by ECO as secondary.

So 20 moves will be used in my research as the base to define an unique opening-line. That finally allows us to check the openings played by my opponents. My personal database of standard games counts today +800. Let us see how often the same 20 first moves are played in those games or complete games if the game lasted less than 20 moves. An hour of scrolling through the database was sufficient to extract the answer out of it. The result was stunning. Only twice I got exactly the same 20 moves of an earlier game on the board. Besides I am pretty sure that these 2 unique cases can be fully linked to very deliberate choices of my opponents. In one game the Dutch IM Edwin Van Haastert copied my lost game played a couple of weeks earlier against the Belgian IM Thibaut Maenhout. It was a full scale battle with many mistakes but the final one was made by my opponent when he missed a devilish trick.

[Event "Interclub Deurne - KGSRL"] [Site "?"] [Date "2006.??.??"] [Round "?"] [White "Brabo"] [Black "Van Haastert, E."] [Result "1-0"] [ECO "B92"] [WhiteElo "2296"] [BlackElo "2400"] [PlyCount "127"] [EventDate "2006.??.??"] [CurrentPosition "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"] 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6.Be2 e5 7.Nb3 Be7 8.O-O O-O 9.Be3 Be6 10.Nd5 Nbd7 11.Qd3 Bxd5 12.exd5 Nc5 13.Qd2 Nfe4 14.Qb4 a5 15.Qb5 Qc7 16.Rad1 b6 17.f3 Nf6 18.f4 Nfd7 19.fxe5 Nxe5 20.Nd4 Rfe8 21.Nf5 Bf8 22.Rde1 { (My opponent, the Dutch International master Edwin Van Haastert noticed in his preparation that I lost only 2 weeks ago a game in this opening. Of course I didn't want to lose the same game over again so I deviated here.) } ( 22.c3 Rab8 23.Rd4 g6 24.Nh6+ Bxh6 25.Bxh6 f5 26.Rdd1 Qe7 27.Bd2 Ne4 28.Bf4 Nf7 29.Rfe1 Qh4 30.g3 Qf6 31.Bf3 Ne5 32.Bg2 g5 33.Be3 Qh6 34.Bd4 g4 35.Qf1 Nd2 36.Qxf5 Ndf3+ 37.Kf2 Nxd4 { (Brabo - Maenhout Thibaut 0-1) } ) 22...g6 23.Nh6+ Kh8 24.Bd1 Bg7 25.Bf4 Rf8 26.Ng4 Ncd7 27.Nf2 f5 28.c3 Rae8 29.Ba4 Re7 30.Nd3 Ref7 31.Be3 Nxd3 32.Qxd3 Ne5 33.Qb5 Rb8 34.Kh1 Qd8 35.Qe2 Qh4 36.Bf4 g5 37.g3 Qh6 38.Bd2 f4 39.gxf4 gxf4 40.Bc2 Rbf8 41.Be4 Qh4 42.Bf3 Rf6 43.Rg1 Rh6 44.Rg2 Rg6 45.Rf1 Qh3 46.b3 Rff6 47.Rxg6 hxg6 48.c4 Rf8 49.Be1 g5 50.Bc3 Re8 51.Bxe5 Rxe5 52.Qg2 Qxg2+ 53.Kxg2 Kh7 54.Rf2 Re1 55.Re2 Ra1 56.Kh3 Be5 57.Rxe5 dxe5 58.d6 g4+ 59.Kxg4 Rg1+ 60.Kf5 Rg8 61.Kxe5 Kg7 62.d7 Rd8 63.Ke6 Kf8 64.h4 1-0

The second unique situation appeared in a game of the club-championship of Deurne. I already once won in 2009 against the 1700 player Pascal Francois. In 2011 Pascal repeated the opening as the opening is theoretically healthy. I agreed as there exists an important difference between the evaluation of the engine and the practical chances in standard play.

[Event "Klubkampioenschap Deurne r1"] [Site "?"] [Date "2011.??.??"] [Round "?"] [White "Brabo"] [Black "Francois, P."] [Result "1-0"] [ECO "B19"] [WhiteElo "2324"] [BlackElo "1736"] [PlyCount "79"] [EventDate "2011.??.??"] [CurrentPosition "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"] 1.e4 c6 2.d4 d5 3.Nc3 dxe4 4.Nxe4 Bf5 5.Ng3 Bg6 6.h4 h6 7.Nf3 Nd7 8.h5 Bh7 9.Bd3 Bxd3 10.Qxd3 Ngf6 11.Bf4 e6 12.O-O-O Be7 13.Kb1 O-O 14.Ne4 Nxe4 15.Qxe4 Nf6 16.Qe2 Qd5 17.Ne5 Qe4 18.Qxe4 Nxe4 19.Rhe1 Nf6 20.g4 Rad8 21.f3 Rd6 { (2 years ago Pascal chose Nd7 in our mutual game.) } ( 21...Nd7 22.Nd3 Nb6 23.c3 Nd5 24.Bd2 b6 25.c4 Nc7 26.Ne5 Bf6 27.Nxc6 Rd6 28.d5 exd5 29.Ne7+ Kh7 30.Bb4 Rd7 31.Nxd5 Rfd8 32.Nxf6+ gxf6 33.Rxd7 Rxd7 34.Re7 Rxe7 35.Bxe7 f5 36.Kc2 Kg7 37.b4 Ne6 38.Kd3 f6 39.Bd6 Kf7 40.a4 Ke8 41.Ke3 a5 42.bxa5 bxa5 43.gxf5 Ng7 44.Bf4 Nxh5 45.Bxh6 Ng3 46.Kd3 Kd7 47.Bd2 Kc6 48.Bxa5 Nxf5 49.Be1 Kc5 50.a5 Kc6 51.Bf2 Kb7 52.Ke4 Ne7 53.Bd4 Nc6 54.Bc3 Ka6 55.Kf5 { (Brabo - Francois,P 1- 0 gespeeld in 2009.) } ) 22.c3 Rfd8 23.Kc2 c5 24.Nd3 Rc6 25.dxc5 Bxc5 26.Nxc5 Rxd1 27.Rxd1 Rxc5 28.Rd8+ Kh7 29.Be3 Rc6 30.Bxa7 Nd5 31.Bb8 b5 32.Rd7 f6 33.Kd3 Ra6 34.a3 Ra8 35.Rb7 e5 36.Rxb5 Nf4+ 37.Ke3 Ra4 38.Rb7 Nh3 39.Bd6 Rf4 40.Rb4 1-0

When we met a third time in 2013, Pacal had learned from the losses. You can't select an opening just by looking at the evaluation of the engine so Pascal deviated much earlier with an interesting alternative.

I want to return to the original question of which openings my opponents play. In the meanwhile we have the answer. Every game a new opening is played except some very rare cases. So we can't predict which openings will appear in the future. Therefore it makes little sense to study the openings of the opponents.

You could even state that it makes no sense to study openings at all at our modest playing-level. That was insinuated in a reaction of the Unknown One see article of 2012. However this is a bridge too far for me. In many openings it is an undeniable advantage to know a number of moves. 20 moves can be a good arbitrary line to define an opening but it tells very little how useful studying openings can be see my recent article the (non-)sense of blitz.

As each opening has its own very specific characteristics, I can't assign one number to the number of moves which one should know to get an opening-edge. Besides this also depends on the knowledge of the opponent as only crucial additional information of the opening will lead to an advantage. Therefore the second part of this article will be covering the effect of studying openings using the scientific approach which I apply in my games. How fast does the opening-knowledge expand when only playing a very narrow repertoire? I have more than 20 years experience with this method, so I can definitely show some remarkable statistics about it. In all those years I played exclusively the same openings and only made adjustments to the repertoire when a line was broken. Below you can see the evolution of my opening-knowledge in the standard games where I was playing white.

There is little difference in the evolution of my opening-knowledge for the black games I played.

In about +400 white and + 400 black games we see an average deviation at move 8-9 compared to earlier played games. In less than 200 of the +800 games I deviated from an earlier game so where I introduced something new which I learned from earlier made mistakes. It is remarkable that we see barely any progress of the deviation during the last 15 years although I kept more or less the same level of activity. So a couple of hundred games is not enough to create depth in somebodies repertoire. I assume my strategy could work for an extrapolated number of games. We saw this in the the project Alpha zero for which 44 million training-games were played. Naturally no human will ever be able to play so many games.

Despite averagely we see a very early deviation in the games, still in a substantial % of games the deviation from earlier played games happens later. I made a graphic about this to illustrate the % of played games linked to the move-number where the deviation happened. Below you see first the graphic of my white-games.

Later deviations occur less frequently in my black repertoire. This has to do with the Dutch opening which I play. White has a large variety of interesting lines in this opening which permits much more early deviations (I mentioned this already in my article a Dutch gambit part 2).

From the graphics we can deduct that in 27% of my white-games there is a duplication of the first 10 moves from earlier played games. For the black games this is only 16%. For the first 15 opening-moves we see that the share of white-games already shrunk to 3% while for the black-games to 2%.

I conclude this long article. The percentages are small but not negligible. Studying the openings of your own games will bring some dividends later. We all have different ambitions and priorities so there exists no rule about which amount of study is reasonable or not. Anyway if you study only for gaining some rating-points then I fear you will get disappointed in the long run.

Brabo