Extending on Third or Fourth Line

    Keywords: Opening, Strategy

This is often the most difficult decision to make, and the answer depends on both what you are extending from and what you are extending towards. Furthermore, it also depends on your overall strategy. Here are some guidelines:

  • If you are worried that your extension may be cut or that your group may come under attack - extend on the third line.
  • If you are worried that your opponent has gained too much influence towards the centre or that you are too low - extend on the fourth line.
  • If you are extending between your own positions - extend on the fourth line.
  • If you have a solid position along the side which you want to use to develop your influence - extend on the fourth line.
  • If you are trying to create a living group or you are invading - extend on the third line.

See also Know Your Lines.

[Diagram]

Black Wins

White has 11 * 11 = 121 points.

Black has (18+11+1) * 4 = 120 points.

Be happy to live with the third line!


JamesA: Just a couple of points... In the diagram above Black has played four moves more than White, which may explain the higher score! Also, I don't think it is a good general rule to use the third line when invading - very often this will lead to a heavy group. Thirdly, I don't agree that when extending between positions you should play on the third line as a general rule - think about the sanrensei fuseki (opening). Last point, if you are worried that your group may come under attack, it's often worth playing on the fourth line to get out into the centre and avoid being sealed in.

Gorobei: Black has actually played the same number of stones as White. Giving the corners to Black is a little unfair, though. My diagram was only an illustration of the surprising strength of the third line (thanks to BigNose for pointing out the break-even line as a concept.)

Goran: I still think Black played more stones :) 13*4 > 12*4

JamesA: Urm, sorry Gorobei but Black definitely has four more stones on the board than White - just count them! The diagram is therefore invalid... that's why I'm pressing the point.

Gorobei: OK, so I was never good at counting :)

HolIgor: Moreover, you can take away four more white stones without changing the score while all black stones work hard. But that is not the point. A third line move really helps to get a basis for a group. Too low but solid.

Storm Crow: I've updated the diagram so both sides have made an equal number of moves. I've seen this diagram done this way in books. Done this way, black has 120 points (one less than white's 121, but it demonstrates the balance of the third line).

Bill Spight: What it illustrates is the inefficiency of White's layout. White has 16 inefficient stones!

The original diagram, with white stones on the fourth line and black stones on the third line, appeared in textbooks to show how central territory is not as big as it looks. Fujisawa Hideyuki pointed out, many years ago, that Black had 8 more stones than White.

In my opinion, that diagram, and its derivatives, should have disappeared from textbooks by now. ;-)

Tjalveboy: Hey, black doesn't win... white has one more point than black, has noone realized?

JamesA: In the diagram below, would anyone be happy taking Black? I wouldn't!

[Diagram]

Bad for Black?


Bill: Suppose that you use 12 stones to surround territory with a single wall.

[Diagram]

Surrounding territory efficiently

You can surround 30 points in the corner, 12 points on the side, and 4 points in the center. Building a wall up to the fourth line on the side makes the same amount of territory as going up to the third line.

What if we use 16 stones to surround territory on the side?

[Diagram]

Third line vs. fourth line, 16 stones

Now the wall on the fourth line surrounds 24 points, while the wall on the third line surrounds only 20 points. Going up to the fourth line is more efficient. :-)

Years ago I read something by Ishida referring to an article in Kido magazine by a mathematician about territory on the side. The most efficient shape for territory on the side is a rectangle with a 2:1 ratio of length to height.

If you make a wall on the fourth line, your opponent may still have room to play underneath on the second line. But with a wall on the third line, you may reasonably estimate the territory by dropping perpendicular lines at the edges.

[Diagram]

Third line efficient shape for territory

That leads to this diagram as the basic efficient shape for a third line wall to make territory. A wall of 6 stones forms a 4 by 2 territory (a 6 by 3 area).

The rule of thumb then, is not to form a longer wall on the third line, or to force your opponent to do so. It also means that it is OK, as a rule, to stretch (nobi) along the third line up to 5 points from the opposite end of your third line territory.

I don't completely buy that argument, but it's good enough for Ishida. ;-)

-- Bill Spight


This is a copy of the living page "Extending on Third or Fourth Line" at Sensei's Library.
(OC) 2005 the Authors, published under the OpenContent License V1.0.
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