The 3-3 Invasion 1 - Introduction

This is the first article in the series “The 3-3 Invasion.”

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The early 3-3 invasion is probably the most front-and-center change that has taken place in baduk strategy since AlphaGo took the world by storm. Nowadays it is studied and played by professional players and amateurs alike. In this series of articles, our goal will be to build a working knowledge of the 3-3 invasion which will be sufficient for you to play with and against it well into dan level. This first article will serve as an introduction to the basic lines of the 3-3 invasion, which will be studied individually in subsequent articles in the series.

Old theory

For the sake of perspective, let us first start with an explanation of the old understanding of the early 3-3 invasion.

This is what was classically considered to be jōseki in the event of an early 3-3 invasion. It is a straightforward tradeoff of territory and outside influence. The reason it was frowned upon as an early-game move is because Black is quite thick. White may have gotten the corner in sente, but is also totally sealed in and the Black tiger’s mouth makes it very hard for White to successfully pull off any operations on the bottom side. The tiger’s mouth also alleviates a lot of the bad aji at the squared cutting point. Since Black’s lower stones have quite a good shape, Black may decide based on the situation to ignore a peep at the cutting point, aiming to settle its two sides separately if need be.

The paradigm shift regarding this position brought about by AI is that the hane-connect is a bad exchange for White. Although it is sente, it is not valuable enough to compare to the thickness White gives away in Black’s tiger’s mouth. Instead, the AI suggestion is that White omit it altogether and tenuki.

These are the possible lines for Black followups if White plays elsewhere. In all cases, as long as White plays correctly, White can make life. Black is still thick, but Black would always have been thick, so there is no opportunity cost. Therefore it is slow for White to spend an extra move here, since the reinforcement is unnecessary, and also slow for Black since ultimately the White corner is not under threat. White can instead tenuki in a way that, in addition to the inherent value of the move, helps to mitigate the influence of Black’s thickness. Leaving the position unfinished also gives White more options to reduce Black’s influence with plays on the bottom side and the aji inherent in Black’s weakness at Q5, whereas previously the strength of the tiger’s mouth discourages such maneuvers.

The ultimate result of this analysis is that the extension after White’s hane at S5 has largely disappeared from high-level opening play. After all, Black wants to do better than not-all-that-much influence in gote. This sets the stage for the new and improved early 3-3 invasion.

The three main lines

The AI-era 3-3 invasion is a fairly complex beast when considered in its entirety. However, for the vast majority of circumstances, you can actually get away with knowing only the basic variations from three main lines:

• the double hane;
• the knight’s move;
• the push.

There is one other major line seen in professional play, but it offers miniscule advantages at the cost of immense complications, and can be totally avoided by both players. We mention it at the end, but we will not devote serious study to it.

The double hane

If Black wants to keep the corner, then Black can use the double hane. This comes at the cost of White getting an outside ponnuki and sente.

The knight’s move

If Black values sente, then Black can extend instead of the hane. Then it is White’s turn to influence which jōseki is played. The knight’s move is a fairly straightforward trade of outside influence and sente for the corner.

The push

White could also choose to extend and invite Black’s hane. After White’s hane Black can tenuki, but also has several options for playing locally. This can lead to a number of different outcomes, some of which are sensitive to ladder considerations.

Keeping it simple

There is a final line worth noting, in which Black plays the knight’s move instead of extending after White pushes. This line is home to many complicated variations that are difficult to play correctly.

Fortunately, neither player needs to know anything about this line if they do not want to deal with these complications. Black can avoid it entirely by not playing the knight’s move, and White can avoid it entirely by transposing to the push line instead of attaching below the knight’s move.

This line sees some use in professional play, but for amateurs the variations can be too complex to use properly as part of a whole-board strategy. There are very few, if any, circumstances in which this line is significantly better than the aforementioned three lines to a degree that matters for amateur play. Certainly at kyu level, it is perfectly acceptable to study just the three simple lines, and avoid this one if it is offered. We in turn will not include it as part of this series.

Conclusion

In this article we laid down the thought process behind the shift in opinion regarding the early 3-3 invasion brought about by AI. We then introduced the three main lines of the 3-3 invasion: the double hane, the knight’s move, and the push. One can play the 3-3 invasion all the way through dan level knowing just the basics of these three lines.

Future articles in this series will begin to examine each line and its variations in detail, explaining the whole-board contexts in which they are appropriate.

Return to the 4-4 Jōseki page.