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Liberty
Path: GiveMeLiberties   · Prev: LibertyIntroductory   · Next: ShortageOfLiberties
    Keywords: Tactics, Go term

Liberty has two different, but related meanings in English.

The first sense of liberty is an empty point adjacent to a single stone or chain of stones. In a legal position each chain has at least one liberty.

This is the basic meaning. Such a liberty is called a dame in Japanese. The liberty - introductory page explains some of the more basic implications in fighting.


Liberty in Chinese is 气 ("Qi" in pinyin), which literally translates to "breath".[1] The thought is that stones need breathing space and that once the last breathing space is removed, the stones die.[2]


A stone or chain may be captured by filling all its adjacent points. Such captured stones are removed before the end of the turn, leaving a legal position. No stone or chain having no liberty is allowed to remain on the board between turns.

A stone or chain with just one liberty is said to be in atari. It may be captured on the opponent's next move.

[Diagram]
Atari

Each of White's stones or chains has a liberty, which is marked. They are not yet captured, and remain on the board.

However, they each have only a single liberty.

[Diagram]
Multiple liberties

Each of these White chains has multiple liberties and is safe from capture for at least two of Black's moves.



The second sense of liberty, important for tactics, is a play required to capture a single stone or chain of stones.[3] This is the sense you require if you want to say that the number of liberties measures time to capture a group.

There are stones that cannot be captured, e.g. stones that are part of groups with two eyes. No number of moves is enough to capture them, they are alive. There are also stones in atari, with no way of saving them. They can be captured with one move. In between there are stones with multiple liberties which may be involved in races to capture.

The easiest liberties to see and count are liberties in the first sense, or dame. The opponent must make at least as many moves to capture a stone or chain as it has dame.

[Diagram]
Example 1: 3 vs. 3

Each marked chain obviously has 3 liberties. It will take Black 3 moves to capture the White chain and likewise, it will take White 3 moves to capture the Black chain. The first player wins this race.

There are also chains where there may be moves which are necessary to capture them on points that are not adjacent to them. Such moves are called approach moves, or perhaps secondary liberties.

[Diagram]
Example 2: 3 vs 3

While each marked chain appears to have only 2 liberties (in the sense of moves to capture them), they each really have 3. Black must connect at the marked point on the edge of the board, while White must take off BS, before they fill a dame in the race to capture. If they filled the dame without making the protective play first, they would put their own stones in atari.

Here again, the first player wins.

The assessment of the necessary moves can get very complicated.

For instance, a one-eyed group is often less close to capture than you'd think.

Here is an example where a big eye has more liberties than are apparent.

[Diagram]
Big eye: 5 vs. 5

Black appears to have only 4 liberties, but actually has 5, the same number as White. This is also a first player win - details in the footnote[4].



The number of moves to capture is normally one more than the number of moves to put into atari, but even then there are comments to make:

  • That isn't true if by putting the opponent into atari you put yourself into atari;

[Diagram]
Mutual atari

The player with the move can capture the other's stones.

  • You may never be able safely to play atari: seki happens;

[Diagram]
Seki

In this seki, or standoff, the opposing chains share two dame, but there are no moves to capture. Whoever approaches puts himself in atari.

  • Sometimes the only way to play atari is a ko capture.

[Diagram]
Approach ko

Black to play can take the ko at a, threatening to capture White's stones. White to play can make an approach move, say at b, to convert to a regular ko. Such a ko is called an approach ko.

Black plainly has 3 moves to capture, but how do we count White's?


Further reading

Authors


[1] This is the same "Qi" as the one considered to be beneficial in terms of Feng Shui.


[2] Bill: Is breath (Chinese) also ambiguous? Or does it only refer to adjacent points?

unkx80: This 气, or breath as you call it, can be as ambiguous as liberty.


[3] This sense may be extended to discussion of groups of several chains, to help answer the question 'how many plays does it take to capture that group?' This is actually a considerably more advanced question, which cannot so simply be answered by inspection. See secondary liberties discussion. -- Charles Matthews


[4]

[Diagram]
Black first

After B7 Black has 3 liberties to White's 2.


[Diagram]
Black first (ii)

Black just wins the race.

[Diagram]
White first

After B6 it is 3 vs. 3.


[Diagram]
White first (ii)

B4 creates another liberty,


[Diagram]
White first (iii)

but White fills it right away.



Path: GiveMeLiberties   · Prev: LibertyIntroductory   · Next: ShortageOfLiberties
This is a copy of the living page "Liberty" at Sensei's Library.
(OC) 2003 the Authors, published under the OpenContent License V1.0.