When to protect your corner?

Laerthd · Post by **Laerthd** » Wed Sep 21, 2016 7:29 am

Quite often in my games, I play 2 stones in a corner and than develop the rest of the board. With handicap games or when I chose to play 4-4, it means that my opponent will probably be able to invade that corner. However I never find it appropriate to spend my move just securing the corner.

Is that a misjudgement of value from my part? When do you usually protect your corner?

Also I don't know if this belong to this subforum or if it belongs to the beginner part so I am sorry if this is not the right place.

jeromie · Post by **jeromie** » Wed Sep 21, 2016 7:41 am

The best time to protect the corner is when the move serves a dual purpose. Often you can build up thickness while preventing another group from getting a base, for example, or as a reply to a corner approach. If that doesn't happen naturally, there are two criteria I would use:

1. When is the outside wall you would get from an invasion no longer valuable? In this case, you want to make any stones you have invested in the corner worthwhile, and you certainly don't want to end up with a floating group of your own.

2. When is securing the corner worth more points than playing elsewhere? This is obviously hard to judge, but if your corner stays open until the endgame it's often worthwhile to secure it in the largest way possible.

sparky314 · Post by **sparky314** » Wed Sep 21, 2016 8:24 am

From a video of Haylee last year, her priority: Urgent - Wide - Big

1. Urgent - You should respond (fights, life and death, approaches - most of the time, etc)
2. Wide - Largest open area of the board (note that this may be corner enclosures, as its an extension)
3. Big - When the widest part of the board is small enough, now becomes a good time to protect the corner. Or make other big moves, such as jumps up to build a moyo.

These are general guidelines. There's also other things to consider, such as invading and reducing - maybe these fall into the "big" category above.

Uberdude · Post by **Uberdude** » Wed Sep 21, 2016 8:27 am

When to protect a corner is a rather deep and difficult subject (I once did an ~2 hour lecture on it and there's lots I still don't know or find hard, for example see around move 29 in viewtopic.php?p=210065#p210065 of a recent tournament game I played where I probably should have protected but didn't, being too hopeful to get some sente exchanges in first). But one simple guideline would be to protect your corner when your opponent invading it would give you a bad position. Are you talking about just 4-4 or also 3-4 corners? One thing I would say is it used to be the established wisdom that 4-4 stones should first make big extensions on the side (on or near star point), and then add a closer move like the knight's move, but nowadays professionals will often enclose the corner with a knight's move first, part of the tighter/practical style of modern Go. There was a nice section about this in GoGameGuru's book Relentless.

How about you show some examples from your games where you didn't know when/if/how to protect a corner?

xed_over · Post by **xed_over** » Wed Sep 21, 2016 1:33 pm

first of all... its not your corner, even if you already have the first stone there.

be willing to trade it for something bigger, or use it for ko threats

Kirby · Post by **Kirby** » Wed Sep 21, 2016 2:09 pm

IMO, these types of questions cannot have general answers, or go would be a simpler game.

You should protect your corner when it is the biggest move to play. It's kind of a snarky answer, but I don't think you can get a better formula.

Bill Spight · Post by **Bill Spight** » Wed Sep 21, 2016 4:11 pm

Uberdude wrote:When to protect a corner is a rather deep and difficult subject

Amen, brother, amen!

Bill Spight · Post by **Bill Spight** » Wed Sep 21, 2016 4:17 pm

If we are talking about playing a second move to enclose a corner, move 3 is not too early, although there are other big plays, as well. Playing a third move to enclose a corner is, in general, a second tier or third tier opening play.

Laerthd · Post by **Laerthd** » Thu Sep 22, 2016 12:28 am

xed_over wrote:first of all... its not your corner, even if you already have the first stone there.

Fair enough, I guess that since I tend not to invade corners often I have the false impression that some corners are mine when their are still an open area.

From the response above, I get that basically adding one stone in a corner is a good idea but in the opening there will probably always be a bigger area to play after that move.

Uberdude, I am mainly talking about 4-4 corners because I never really had the problem with 3-4 corners but maybe this is due to the level I am playing at or playing on IGS instead of tygem. As for the game you linked, I would never have thought of protecting my corner this early in the game. Although looking at the position, I want to attack the lower left corner so I guess it is natural that the opponent finds it appropriate to attack yours.

Trying to provide a concrete example, I've looked at the games that bothered me and I think the problem is I don't realize the huge number of points that a corner invasion has. It seems to shift the score by 15-18 points each time so I should clearly prioritize this over 4-point yose.

Uberdude · Post by **Uberdude** » Thu Sep 22, 2016 12:48 am

Laerthd wrote:Uberdude, I am mainly talking about 4-4 corners because I never really had the problem with 3-4 corners but maybe this is due to the level I am playing at or playing on IGS instead of tygem. As for the game you linked, I would never have thought of protecting my corner this early in the game. Although looking at the position, I want to attack the lower left corner so I guess it is natural that the opponent finds it appropriate to attack yours.

Because of black's nearby supporting stones (r10/o17/l16, plus he has ladder to lower left which makes my q15 at r15 have an annoying cut) his invasion at the upper right is not only a territorial move, it is also an attacking move, taking away my base in an area I can't then make a comfortable extension. On the other hand white's invasion at the lower left is far less powerful as I don't have that nearby support. In the game when I played it it was a rather desperate attempt to make a big ko.

Laerthd wrote:Trying to provide a concrete example, I've looked at the games that bothered me and I think the problem is I don't realize the huge number of points that a corner invasion has. It seems to shift the score by 15-18 points each time so I should clearly prioritize this over 4-point yose.

More like 30 points as a ball-park figure! To take my game upper right example, if white defends it makes about 15 points in the corner, versus black making 5 or so. But white's move at q18 also has a large effect on black's top side, e.g. m17 invasion. Plus the taking the base is often important too. In such cases the invasion is often sente rather than gote. A 30-point sente move is huge.

Bill Spight · Post by **Bill Spight** » Thu Sep 22, 2016 1:57 pm

Here are some positions to consider.

Go to :b41:

. This move secures the corner, makes territory, protects the Black stone on M-17, and attacks the White group. A multi-purpose move!

Go to :w26:

. The fact that White invades indicates that this is a good position for Black to enclose the corner, if it were his turn. This is a good example of a second or third tier opening move.

Go to :w12:

. This is another case where the invasion indicates that enclosing the corner would be good, if it were Black's turn. The enclosure would not only stake out territory, but strengthen the Black framework on the top.

Go to :b23:

, then to

. Black plays :b23:

as the second enclosure stone that also attacks the R-11 stone. After that, both players find the rest of the board more interesting that the top right corner, even after White approaches it with :w70:

. As Uberdude says, when to play the third enclosure stone is not always obvious.

sybob · Post by **sybob** » Mon Oct 03, 2016 1:45 pm

Question to self: am I trying to be serious, or trying to be funny?
My 2 cents: I'd say the best moment to secure 'your' corner is 1 move before the other player would have played it.

tchan001 · Post by **tchan001** » Tue Oct 04, 2016 5:50 am

If you can get a big enclosed moyo while keeping the opponent contained with small territories in the corners, you probably wouldn't protect the corners at all. Probably difficult to achieve at higher levels but definitely possible at lower levels. I have had a couple games where I have won despite the opponent controlling all the corners along with having a small center territory.

Unusedname · Post by **Unusedname** » Wed Dec 14, 2016 3:40 pm

jeromie wrote:The best time to protect the corner is when the move serves a dual purpose. Often you can build up thickness while preventing another group from getting a base, for example, or as a reply to a corner approach. If that doesn't happen naturally, there are two criteria I would use:

Here's a trick to make it occur "naturally".

When your opponent has one stone on the side, consider which side you play your checking extension.
Push them towards the corner you want to defend and ta da! you've made your own dual purpose move.

RobertJasiek · Post by **RobertJasiek** » Thu Dec 15, 2016 12:05 am

The thread is in the forum for amateurs but the answer also applies to professionals. The question is general so the answer must be general.

Make a positional judgement of the current position. Consider candidate moves, among which those of a local move selection of a defense of the corner are included. For each candidate move, develop good global variations resulting in follow-up positions. For each (quiet) follow-up position, make a positional judgement. Due to the variations and positional judgements, derive or update the positional judgement of the current position and make the fitting tactical and strategic choices.

A local move selection considers all possibly interesting local moves and chooses the most interesting ones for further consideration.

Positional judgement of a position assesses the static aspect of current territory and the dynamic aspects of statuses of connection, life, stability, life of possible invasion groups; neutral stones, development directions, reductions, invasions, aji, thickness, influence, local potential, their best use, fights (incl. attack, defense and their combination). In particular, also consider all interesting reductions, influence-reductions and invasions of the particular corner.

Only a global analysis incl. all the mentioned aspects reveals the answer.

Life In 19x19

When to protect your corner?

When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?

Re: When to protect your corner?