Welcome back to part two of our three-part Go tutorial.
In this part we will fill in some essential areas that
you will want to know about to get ready to play actual go games.
First we'll return to the special rule we alluded to in Part 1, called the "Ko" rule,
which basically just prevents the game from getting into an infinite loop.
This situation does not come up in every single game,
but it is common and you can expect to run into it before you've been playing Go very long.
What the Ko rule actually says is that you can't
return the board back to the exact position it was in on the previous move.
In this example, black is able to capture the white stone.
But in doing so, the black stone also ends up with just
one liberty and could otherwise just be captured right back.
The rule against putting the board back in the same position forbids this,
since if this were allowed it could just go on forever.
Let's say, then, that white really wants to recapture the black stone,
in order to connect the white groups on the right.
After black's initial capture, in order to get around the limitations imposed by the Ko rule,
white needs to find what's called a "ko threat".
This is a move, somewhere else on the board, that pretty much forces black to respond over there -
for instance, this move threatening to capture the black stones in the corner.
When black does respond, white can recapture the ko since the board has changed since the last capture.
Now it's black's turn to try and find a ko threat.
This can still go on for several rounds, but since the board is changing each time
eventually there will come a point where one side can't find a big enough ko threat,
and the other side just connects their stones and settles the position.
It's also important, though, to point out what's not ko.
Remember that the ko rule only forbids repeating the exact same board position, not recapture in general.
Cases that fall under the ko are are those where one stone captures one stone, like the example that we saw.
If, however, one stone captures several stones an immediate recapture is perfectly legal,
since the board is not returned to its previous position.
Likewise, if several stones capture one stone
in a way that leaves them with just one liberty
they also can be immediately recaptured.
Again, the board is not put into an infinite loop.
Next we'll describe how you actually finish the game.
When a player can see nothing useful to do on the board -
they can't surround any any more territory or capture any more stones,
and don't need to prevent the opponent from doing so - they can pass instead of playing a stone.
If the opponent agrees they can also pass, in which case the game is over and you count up points.
If the opponent thinks there is still something to do, though,
they can play a stone instead of passing, in which case play resumes as normal until somebody passes again.
In this case for instance, white is behind on points but sees that black has left a weakness.
White ends up capturing a couple of black stones.
Now when both sides pass, white ends up ahead.
So don't pass until you're sure the game is over;
otherwise you just lose a turn.
Of course, a player who is hopelessly behind can resign,
but make sure it's really hopeless before you do that.
Many a Go outcome has turned on unexpected events late in the game.
Here we need to mention an alternative scoring method.
We won't go into the details but we need to touch on it briefly because it affects the ending of the game.
The scoring we described in part one, and which you'll encounter most often,
is called "territory", or "Japanese", counting.
There's another method called "area", or "Chinese", counting, which you'll sometimes encounter.
If you're using area counting, you should use your last few turns
to fill in the empty points that are between the opposing groups before you pass.
For instance, if we go back to our sample game
the triangle points here are the ones you would need to fill in.
These are called "dame" points.
In territory counting these don't count for either side since they aren't surrounded.
But in area counting having stones on these points does add to your score.
In this process one thing comes up often enough that a warning is in order.
When you start filling in the dame points, your groups are losing liberties;
you need to make sure that this doesn't turn into a problem.
For instance, the last white play put black's upper-right corner in danger.
If black were to pass, and white played at triangle, the group would be captured.
So black needs and extra move to make sure that these white stones stay dead.
One topic you'll quickly encounter when you start playing Go is that of ranks.
Ranks are not just to label to describe a player's skill level,
but are a key part of setting up a game because Go, unlike chess and similar games,
has a very workable handicap system.
There are several ranking systems in use in different parts of the world,
but the ones you'll usually run into work this way:
there are two divisions of players, "Dan" is the higher division, "Kyu" is the lower one.
The Dan levels are numbered starting from 1 Dan and going up to 9 Dan, the strongest.
Kyu levels or also numbered, but the numbers are inverted.
The strongest Kyu players, just below 1 Dan, are 1 Kyu.
The next level down is 2 Kyu, and so on.
Ranks generally go down to about 30 Kyu.
So if you look at the whole range of ranks,
you can generally think of somebody below 20 Kyu as a beginner.
and in the teens as an advanced beginner.
Single-digit Kyus are intermediate level players.
1 to 6 Dan's are advanced players,
and the top several ranks are expert.
In describing ranks, we should mention professional ranks, which can be a source of confusion.
Players who turn professional are all from the top, expert, ranks.
What's confusing however, is that professional ranks are also called "Dan", and are also numbered 1-9.
So if you see "1 Dan", for instance, you need to know, often just from context,
whether it's regular 1 Dan or professional 1 Dan.
A professional 1 Dan is already a high-dan player in terms of standard rankings.
Professional ranks are actually more like titles, which were awarded by certification committees
based on their evaluation of the player's understanding of the game.
Standard Dan and Kyu ranks are strictly statistical, based on previous game results.
So, ranks are a guide by which anyone, at any level, can enjoy a fun and challenging game of Go;
just match up with somebody your own rank.
Setting up a good game of Go is made even easier, though, through the handicapping system - it works this way:
If two players of the same rank play a game, the player who takes the white stones
will get some compensation points, called "komi" to make up for going second.
Usually komi is set to six and a half points;
this gives each player a statistically even chance of winning.
(Notice that the half point makes it so that you can never have a tie.)
In this case, it doesn't matter which side takes which color.
If one of the players of one rank stronger than the other,
the stronger player will take the white stones, but not take a komi
(or, often, there's still half-point komi to prevent ties.)
This gives black the small head start and makes the game fair again.
If the difference in ranks is larger than 1,
then the stronger players still takes the white stones - still without komi -
but now black gets to put extra stones on the board before the game begins.
If the difference is two ranks, black puts two stones on the board before white gets a move.
If it's three ranks, black puts three stones on the board, and so on.
This handicapping scheme generally is useful up to about nine ranks.
Finally, we'll say a few words about the flow of a game and how a game develops.
New Go players almost invariably get off on the wrong foot in one of two predicable ways:
either they go all-out to try to capture some stones,
or they try to immediately start forming solid groups that they're sure can make two eyes.
Neither of these very efficient, and a few tips now will help you bypass these mistakes
and play a much better game from beginning.
Think of the game initially as staking out territory (territory is, after all, the goal of the game)
so it's very common for both players to use their first moves to stake out the four corners, something like this.
After this, you can try to expand your claim or challenge the opponent's claims.
This is something of a challenge move.
Now that black is closing in, white will probably want to play his next move somewhat close,
lest his stone become overwhelmed.
Now, black may be feeling that the previous move is in danger of becoming outnumbered,
and might play something like this move to reinforce it and link back to the corner.
It's white's turn now to challenge black.
If black responds really closely, as in actually touching the white stone,
then white will want a friendly stone also really close, probably also touching.
Neither side has directly tried to form living groups, but if you look at the board
you'll see that groups are starting to take shape from the initial staking-out of territory
And neither side has directly tried to capture anything,
although the threat of capture has influenced the moves so far
(and there will almost certainly be captures as the game develops.)
And that's about all you need to know to sit down and start playing.
If you don't already have a ready place to find an opponent,
you can go to one of the online Go servers such as KGS, shown here.
And after you've tried Go out a bit,
we hope you'll come back and join us for Part 3 of the tutorial,
which will teach you terms and concepts you'll need for your ongoing Go study.
We hope to see you at the Go board.