Attachment on the second line

Contact play  

Once Black attaches at , two common responses for White are a and b.

White wants thickness  

is a solid line of play. Black gets additional territory and White gets solidity facing the right hand side.

This works well for White when White has stones to the right at a or b. White stones closer than that would yield an overconcentrated shape.

Alex Weldon: If the White stone is much closer (say at c, especially if the ladder towards the upper right is good), or if Black is playing this too early in the game, and White is willing to play lightly, it may be possible to omit . This would make the sequence gote for Black.

White wants territory  

If White chooses to capture with the hane at , forces White to play to complete the capture of .

Black will then roll over top of White with . Black obtains outside thickness, while White gains some territory. For White to resist by playing there herself is inconsistent with .

Velobici: Such is this 10k's understanding. Please correct my errors and enrich this page.

Charles I saw a 4 dan and a 7 dan discuss this, last year. The 4 dan said he'd automatically play above; the 7 dan commented that the 4 dan needed to change his entire attitude to the game. So, who am I to comment?

Actually, this is one of the most basic middlegame joseki. Even so, you have to look at crawl lines to understand the local tactics.

Crawl  

Here is natural resistance.

Black has several choices: at a, at b and possibly some ways to fight out with .

Continuation  

If Black avoids complications, up to is expected.

Clearly here White has played in a territorial way, and Black has gained in influence.

Low  

Bill: For instance, through Black is too low.

Not in Gobase  

Bill: I did a little database searching on GoBase, and no instances of this pattern showed up. You have to have other stones in the vicinty for the pros to play .

Defense  

Bill: The database guys can check this out, but one of the commonest situations where this attachment occurs is as a defense when separates the two Black stones.

Kikashi  

Bill: Another common use for this play is as kikashi against Black's corner enclosure. The clamp at also occurs frequently in other contexts, especially where White wants to play lightly.

Endgame move  

unkx80: This second line attachment is also commonly seen when there is a one-space jump stone, and can be a very big early endgame move.

Endgame move  

unkx80: If gives in, then gains a substantial amount of territory. Later, Black can aim for a or b, which may cause to immediately patch up this weakness, allowing Black to gain sente.

Endgame move  

unkx80: If resists, then and can push into White's territory on the right. Whether Black's sacrifice of is properly compensated by the breaking in by and depends on the wider context.

Moves 78 to 87  

In reply to , builds strength. White is defending, but now there is a chance of White a to cut in the centre. (From An Younggil-Ch'oe Myeong-hun (B) 2001-06-07.)

Moves 88 to 97  

Again White plays contact with . This time Black answers solidly with , to keep up the attack.

Moves 98 to 107  

In the end strengthens the centre. Here attack and defence are well balanced.