British Go Journal No. 2.  Autumn 1967. Page 23.
Part 1 of this series is on page 7 of BGJ 1 .
From the experience of players first introduced to Go it appears that the most difficult idea to understand is the general idea of "territory".
A territory is an area claimed by one player when his stones surround it so that he can form, with proper play, two eyes and his opponent cannot. The size of the area, the shape, and the strength of the outside wall must all be considered in deciding if it is safe.
As far as shape is concerned, long narrow areas are better than square ones. A formation surrounding four points in a row is safe no matter who plays first, whereas one surrounding four points in a square cannot form two eyes there in any case.
The strength of the outside wall must be weighed in forming territory. A formation of black stones on the tenth lines, surrounding a quadrant is said to form a safe territory, for white cannot form two eyes if Black plays correctly. Try it and see.
There are several widely accepted principles on where and how to form territory, and the first is:
It is easiest to form territory in the corner, harder along the sides, and hardest of all in the centre. This can be easily seen from the minimum number of stones needed to form two eyes; 6 in the corner, 8 along the sides and 10 in the centre.
Thus the basic principle of strategy is to play first in the corners - either closing a corner with two stones, or attacking an enemy play in the corner - then to build territory along the sides, and finally extending into centre.
The methods of forming territory in the corners are mostly joseki studies, and the beginner should gain some knowledge of these before anything else. Here we shall consider the methods of forming territory along the sides.
In extending along the sides form a corner position the questions to be asked are: (1) How far up form the edge? and (2) How long a jump form the corner?
Primarily, you should play along the third line to form territory, but with some stones on the fourth to ensure that you can prevent your opponent form grabbing all the centre. This is the second basic principle of forming territory.
Diagram 1 |
Before 1930 classical play emphasised the third line heavily. But in the 1930's a new opening strategy was proposed (Shin Fuseki). These two are contrasted in the opening in Dia 1 with Black playing the extreme form of the new strategy. These fourth line plays are designed for central influence more than immediate territorial gain.
The White plays are an extreme form of the classical style. Such a heavy accent on the third or fourth lines alone is rarely seen now, and the modern style is rather a mixture of the two, taking the best points of each and forming a "balanced" style.
Diagram 2 |
The search for balance is well illustrate by the example in Dia 2: Black plays 1, low relative to . If was at A, the best play would be B, balanced with the low play at A.
In the opening in Dia 1 you may have noticed that Black played one stone in each area, and on the very points that handicap stones are placed, but it takes considerable skill to follow this up profitably.
Again referring to Dia 1 and bearing in mind that no one additional move can secure the handicap corner, good plays are A, closing the corner; B, taking side territory; and C, aiming in either direction. This last play is very strong and should be used more often in handicap games.
Diagram 3 |
In forming territory, the biggest question to answer is, how far to extend from the corner groups? The widest extension usually used is 6 points, Dia 3 for example. The safe extension from a single stone on the third line is two points, forming a connection that cannot be broken.
Diagram 4 |
The example in Dia 4 illustrates the use of extensions: Moves 10 and 11 are large extensions, 12 and 14 are safe extensions.
What is the thought behind 10 and 11? The opponent can invade directly in the gaps left behind. But note that if White plays A, Black can safely extend to B, leaving White squeezed between two strong black groups. White has made a similar move with 14, threatening blacks corner as well. One reason for Black playing 13, and not C, is that he would not have this optional extension.
The 5 point extension, 10 and 11, can be consolidated with a further play at D or A, but it is more likely that E, or more commonly, F will be played. This latter play threatens to form a "box" formation with G which is very strong and is almost irreducible.
However the beginner is usually more interested in knowing how far he can safely extend without fear of being disconnected, and in knowing how he can capture the invading stone if he has to.
In most circumstances one can extend, on the third line, two points from a single stone, three from two stones, four from a three stone formation etc. [Examples referenced, but references didn't work.]
It is all very well to say that a certain extension is normal and safe - but what to do when your opponent disregards this and plunges in? A beginner often learns how to make the right move, but not how to defend it; he becomes discouraged and retreats to timid extensions, which are even more certain paths to defeat. Naturally, there is no simple answer to this, but the following may suggest an approach.
Diagram 5 |
Consider this situation; Black makes the extension to 1, whereupon white invades at 2. What should Black do?
First Black must decide whether to capture the white stone or will he force White out into the centre, making a strong wall to the right. In many cases, the latter is more profitable, but if there are white stones to the right Black must capture as Black cannot expand profitably to the right. Should then Black attack with A, B or C?
Diagram 6 ||
Diagram 7 |
The one play he should not make is 1 in Dia 6. Dia 6 indicates the kind of complication that White can devise. Instead, Black should play Dia 7, giving White little choice beyond the sequence shown on the right. 5 is the key play and once you have learned this type of capture it seems simplicity itself, but many a beginner plays timidly at 6 instead, and White is out. 9 captures White, with no opportunities for ko or anything else.
It is good for Black to study such possibilities by himself, so that he is prepared to defend his territorial claims. But in any case, if he knows that his extension is right, he should play with a certain aggressive confidence against any unorthodox white plays.
Diagram 8 |
[BGJ had black 1 on third line. === sgb]
The same thing applies to larger extensions, the similar sequence for the next larger extension from the 4 stone wall to , invaded at is shown in Dia 8. After this last play white can only push in one point to A, and he has also stranded three stones with no base in a powerful black formation.