| Position 1 | Position 2 | Position 3 |
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| Solid connection | Diagonal connection | Weak point |
Definition:
Weak points in a territory are points which still demand some attention and have to be considered before passing.
At least, this is how we will define weak points within the narrow context of this Supplement. Such points can be divided into two categories: the ones that definitely need to be strengthen, and the ones that ultimately can be left alone.
As a group, most weak points are relatively easy to recognize. They are the points at which the chains of your stones composing the fences are connected diagonally. The difficulties lie in deciding into which of the categories a given weak point belongs. In other words, answering the question "Do I still need to play there?" can be hard, in some circumstances.
But first, lets look at some weak points without worrying too much about the details.
As stated above, most (potentially) weak points can be recognized by the fact that the stones are connected diagonally rather than solid. What's more, most of the time one side of such diagonal connection will be occupied by an enemy stone. So lets review all such kinds of connections, just as a reminder (you can read some more about connected and cut stones here.)
| Position 1 | Position 2 | Position 3 |
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| Solid connection | Diagonal connection | Weak point |
First, lets look at Position 1 of Figure 1. We can see a solidly connected row of 4 stones, no weaknesses there. When your stones are connected like that, there is little need to look for weak points - there are none! Case closed. Lets move on.
In Position 2 of Figure 1 we see a similar configuration of 4 black stones, but this time they are not all connected in a solid manner. The connection between the two marked stones is diagonal. By itself, this is not yet a reason to panic, but you should still pay some more attention to such connections. In this particular situation, there are no enemy stones around, so the connection, even if not solid, is sound. This is because of the miai situation (explained in a different context here). In short, miai means that there are at least two points which fulfil the same function. Such points are called miai points and you can observe one example of them here - both points marked 'a' are miai - which means if White plays on one of them, Black can take the other and thus complete a solid connection.
Now, lets look at Position 3 of Figure 1. As you can see, the black structure is exactly the same as in Position 2. However - there are now some white stones around. In particular, there is the marked white stone which occupies one of the miai points explained above. This makes the point 'b' vulnerable. This makes is a weak point!
Of course, not every one of such points needs to be firmly connected by Black. Remember, each such connection within one's territory loses one point - since it diminishes the empty points surrounded by the player (using area scoring, explained here, such moves can also lead to loss of a point since the opponent can play on a neutral point and thus gain a point.) This means that such weak points should be considered, but not necessarily automatically defended. This is where tactical evaluation has to take place.
According to what I said above, there are two categories of weak points. Ones which definitely need to be defended, and ones that do not. Simple, no? But there is a lot of thinking needed to distinguish between these two categories. First, lets look at some of the easiest examples in the first category.
The most basic weak points within your structures are easy identifiable - they are the ones next to stones which will eventually be vulnerable to capture once outside liberties are filled out. Lets look at some examples.
| Position 1 | Position 2 |
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In both Position 1 and Position 2 of Figure 2, the point marked 'a' is a weak point in Black's structure. What's more, the weakness of that point is immediately exploitable by White. If White plays at 'a', the Black marked stone will be captured, and White will reduce Black's territory. So, in both cases, Black needs to defend by connecting at 'a' to avoid loss of points.
A slightly more complicated situations are given in Figure 3. Lets have a look.
| Position 1 | Position 2 |
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In both the above positions of Figure 3, Black is in no immediate danger. If White should play at any of the points marked 'a', Black will be able to capture the white stone and gain a point. So, White will not be able to play there as it stands.
However - what if White first plays at any of the points marked 'b'? The positions will then transition neatly into their counterparts from Figure 2 and Black will be in immediate danger again. And so the need will then be immediate for Black to defend! See?
The point is here that even if Black is in no immediate danger as it stands in Position 1 or Position 2 of Figure 3, the need is eventually unavoidable - which is just another way of saying that White cannot be prevented from eventually playing at 'a' and putting Black in danger. So, if Black does not see any other worthwhile moves to play, playing at 'b' is a good idea - since 'b' has to be defended eventually anyway, so might as well do it now. Why wait for White to play at 'a' and put the marked stones in danger? This kind of thinking is often seen at the end of a Go game.
Caution:
Playing defensive moves (like at 'b' in Figure 3) has a price of effectively losing one's turn.
This is not desirable, in general, and therefore great care should be place on determining if there are any other
good points to play at before making such defensive moves ahead of schedule.
If the need is immediate (as in Figure 2), then its another story, and defending is usually advisable.
And now, one last example of weak point, this time also an immediate danger, but slightly more complicated. I will not give any comments to this position - please try to work it out for yourself why a defensive move is required. If you need some help, this kind of stuff is discussed here.
| Position 1 | Position 2 | Position 3 |
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| Initial position | White goes first | Black goes first |