Charles Matthews Although there is much already written here about thickness, and allied concepts such as influence, I'm not at all convinced by it. One has to master, not just some definition and advice, but recommended and deprecated linguistic matters as well as recommended and deprecated strategies.
For a reasonably fresh start after reading Thickness / Discussion again, I'm going to use the analogy of one of those biochemical cycles that metabolise (say) a sugar.
That is, we know what comes out the far end of successful strategy: territory. According to the Thickness / Discussion page, there is an important conversion step we can call
Thickness I -> Thickness II
at the heart of pro-level thinking. Here Thickness I is atsumi in Japanese, while Thickness II called atsusa is a higher-level concept. That is, Thickness II may be what you want but Thickness I is the precursor (perhaps not the only source).
Let's write down some steps in this style and mark them as recommended, deprecated or neutral judgements.
Joseki -> Thickness I (neutral).
That is, you may choose a joseki giving you thickness in the most clear sense.
Thickness I -> territory (deprecated).
That is, with that early acquisition of a thick position you shouldn't look for points straight away.
Thickness I -> flanking extension -> framework (recommended)
That is, a flanking extension from a thick position is good, but not because it takes immediate territory. The extension to a good distance should produce a worthy framework. The extension is there to prevent the opponent from establishing a strong group placed in a way to negate the effectiveness of your thickness.
Framework -> omoyo -> ippoji (deprecated).
Don't think solely in terms of expanding frameworks on the largest possible scale. This can be wrong in principle for a couple of reasons:
- exchanges such as pushing your opponent along the fourth line cost points (see fifth line), even if they build up a framework too;
- the argument against ippoji is that you may have to kill an invading group to win, rather than pursue a 'collateral damage' plan.
On the other hand
Framework -> opponent invades -> Thickness II (recommended)
means that one way to get an overall thick position is to play for a 'second phase' after your initial framework is invaded. This idea is built into the use of 4-4 point openings, for example.
Trying to kill the invasion:
Invasion -> chase towards Thickness I -> attempt to kill (neutral)
has to be judged on merit. Thickness I is exactly what you need to kill groups with: but trying too hard to do that is the amarigatachi mistake. The alternatives are like
Invasion -> chase -> create Thickness II (recommended) Invasion -> chase -> splitting attack (recommended).
Simply starting a running fight is probably too 50-50 if you had a thick local position - but it happens with some frameworks, and you have to go for central power.
If there is really no good direction of play after an invasion of a framework then there is a problem of some strategic kind, related to false thickness, or an initial framework that was too broad, or set up in the face of the opponent's strength.
In the end you are supposed to do
Thickness II -> better overall position -> milk the endgame.
This means that skilful players know how to use Thickness II to take profit here and there. You make the opponent defend weak groups and weak territories.