Jōseki

Jōseki are not fixed but comprise patterns that have gained acceptance in professional games; they constitute a consensus that may change with certain caveats. Hence, the basic definition may be misleading for new players in that a jōseki can be misconstrued as foolproof and unalterable and as optimal for all situations. Many jōseki are in fact useful only for study within an artificially confined corner,[1] and in real play are only considered good form when used in proper combination with other plays on the board (i.e. other jōseki and fuseki moves).

Knowing a particular jōseki simply means that one knows a sequence of moves, resulting in a balance or fair trade-off between black and white positions. This is in practice much easier than appraising how jōseki relate to the rest of the board – hence, knowledge of jōseki is regarded as shallow, when compared with the ability to integrate a strategy into a complex game landscape.

One go proverb states that "learning jōseki loses two stones in strength," which means that the rote learning of sequences is not advantageous; rather, learning from a jōseki should be a player's goal.[2] Hence, the study of jōseki is regarded as a double-edged sword and useful only if learned by understanding the principles behind each move, instead of by rote. Every jōseki should be used as a specific tool that leaves the board in a particular shape.

Just as using an improper tool in machinery can be devastating, choosing the wrong jōseki can easily be worse than improvising one's own moves. In his book A Way of Play for the 21st Century, Go Seigen compared choosing the proper jōseki to choosing the proper medicine: "Pick the right one, and you feel better. Pick the wrong one, and you die." [par.] Rui Naiwei similarly remarked that "playing joseki is easy [but] choosing the right one [in a game] is hard." [par.]

A jōseki may fall out of use for various reasons, some of which may often seem minor to the amateur player; professionals may consider one variation suboptimal for a very specific reason – one which strong amateurs are not likely to exploit. There is no definitive guide to what is a jōseki; the situation with jōseki dictionaries is similar to that of natural language dictionaries: some entries are obsolete, and the list is likely to be incomplete.

Corner jōseki conventionally start with one player occupying a corner point, in an empty 19×19 area of the board, and the other player replying with an approach move (Japanese: kakari). The initial play in the corner is almost always on a 3-3, 3-4, 3-5, 4-4 or 4-5 point. Other plays that have been experimented with include 5-5, 6-3 and 6-4, all of which sacrifice territory for influence.

Of those plays, the classical 3-4 point (komoku) and more contemporary 4-4 point (hoshi) are the most used. The standard approaches are at 5-3 or 5-4 to the 3-4 point, and at 3-6/6-3 to the 4-4 point. The number of subsequent variations is then quite large (of the order of ten reasonable plays for the next one).

A Go game opening with two common jōseki in the upper-right and lower-left.

Breaking away from a sequence to play elsewhere (tenuki) before the conventional endpoint of the jōseki is not uncommon in higher level play. There is no formal theory for follow-up plays after jōseki, though numerous set sequences can be seen in professional play.

It is imperative that players should not play a jōseki merely from rote memorization but adapt according to the overall board situation. It is important to keep in mind that go is a game involving marginal analysis and jōseki are merely heuristics of sound play. Playing jōseki blindly will not improve one's game.