Double-purpose plays
Any play that has two meanings, regarding tactics or strategy or both. For example double atari, or a play that defends your group while attacking your opponent, or a good ladder breaker that has some effect. Another tactical example is the double threat ladder-maker.
- Focal plays are strategic double-purpose plays relating to two frameworks.
- Karami is a technical term for double-purpose attacking plays that cut off and separate the opponent's weak groups, known also as splitting attacks.
Much of basic strategy aims at setting up double-purpose plays, or denying them to your opponent. See for example immediate life. Clearly they are in general useful, and a sign that you are co-ordinating different objectives. Sometimes they are also cases of the miai concept, but certainly not always.
However, you should be wary of reaching too hard for dual-purpose plays - finding moves that try to do two things at once, but do neither of them well. A true double purpose move doesn't compromise on either of its goals.
This is a partial position from a game. connects, builds a moyo and protects the corner, but achieves at most one of these purposes satisfactorily. Playing a to take territory (and build the moyo) or b to build the moyo (and connect) are probably better.
To me (10k?) it seems fairly obvious that a move in the fourth unoccupied corner would be multi-purpose for white, looking toward making territory and connecting to one or both existing white groups. I therefore want to play there as black to forestall that. I'm not sure exactly where.
This could lead to a sequence like the diagram below, though, where white has reasonable places for 4 at b, c or around d.
Is going into the corner an error, or just another way to play? How should black handle the follow up? Should he use 3-3 as the 1st move in the corner so an approach move is not sente?