Life In 19x19 :: What is the difference between Reduction and Invasion?

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What is the difference between Reduction and Invasion? http://www.lifein19x19.com/viewtopic.php?f=11&t=11625	Page 1 of 2

Author:	DiogoBarbosa [ Thu Mar 19, 2015 8:27 pm ]
Post subject:	What is the difference between Reduction and Invasion?
Hello, I was reading about Reduction and Invasion on the Sensei's Library. http://senseis.xmp.net/?Invasion and http://senseis.xmp.net/?Reduction But I did not understand the difference between them. Some people tried to explain to me in the OGS chat, but I have not found difference between the concepts yet. Please, Can anyone help me? Thank you a lot.

Author: Kirby [ Thu Mar 19, 2015 8:44 pm ]

Post subject: Re: What is the difference between Reduction and Invasion?

On the page you linked, here was a diagram for reducing:

Click Here To Show Diagram Code: [go]$$W $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . O . . . | $$ | . . . , . . . . 1 , . . . . . . O . . | $$ | . . . X . . . . . X . . . . . X O . . | $$ | . . . . . . . . . . . . . . X . X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

White is not trying to live or split black on the side. Black can simply block, and he will still get territory on the bottom:

Click Here To Show Diagram Code: [go]$$W $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . O . . . | $$ | . . . , . . . . 1 , . . . . . . O . . | $$ | . . . X . . . . 2 X . . . . . X O . . | $$ | . . . . . . . . . . . . . . X . X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

But the idea is, white has reduced black's potential to make more territory in the area. For example, if they continue simply:

Click Here To Show Diagram Code: [go]$$W $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . O . . . | $$ | . . . , . 7 5 3 1 , . . . . . . O . . | $$ | . . . X . . 6 4 2 X . . . . . X O . . | $$ | . . . . . . x x x x . . . . X . X . . | $$ | . . . . . . x x x x . . . . . . . . . | $$ ---------------------------------------[/go]

White is conceding to allow black to make points in the marked area - but not higher than that. For example, if black had played first:

Click Here To Show Diagram Code: [go]$$W $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . B . . . . . O . . . | $$ | . . . , . x x x x , . . . . . . O . . | $$ | . . . X . x x x x X . . . . . X O . . | $$ | . . . . . x x x x . . . . . X . X . . | $$ | . . . . . x x x x . . . . . . . . . . | $$ ---------------------------------------[/go]

Black may end up getting more points in the area. By reducing, white reduced black's potential in the area.

---

Invading, on the other hand, is not about conceding points to your opponent. It's about trying to take away points in that area completely, either by living there yourself, or by splitting them up.

For example, it may not be a good move, but this is an invasion, from the same position:

Click Here To Show Diagram Code: [go]$$W $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . O . . . | $$ | . . . , . . . . . , . . . . . . O . . | $$ | . . . X . . . 1 . X . . . . . X O . . | $$ | . . . . . . . . . . . . . . X . X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ ---------------------------------------[/go]

Assuming white lives, black won't have many points in the area he did from the reducing variation. For example, assume black plays in a slack and simple way - just to show a simple variation.

Click Here To Show Diagram Code: [go]$$W $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . 5 . 4 . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . 3 . 2 . . . . . O . . . | $$ | . . . , . . . . . , . . . . . . O . . | $$ | . . . X . . . 1 . X . . . . . X O . . | $$ | . . . . . . . . x . . . . . X . X . . | $$ | . . . . . . . . x . . . . . . . . . . | $$ ---------------------------------------[/go]

It's hard to say that black has gotten points in the area on the bottom of the board, because white has established a presence there.

---

Generally speaking: Reducing concedes more to the opponent - kind of like negotiating. It's like, "you can have this many points here, but that's it. I'm reducing your potential, and you just keep that area.

Invasion, on the other hand, is less about conceding, and more like, "move out of the way. I'm breaking this area up so that you don't get territory here."

You may take away more of your opponent's points with invading, but reducing is safer, since it's less likely the opponent will try to kill you.

There are exceptions to the definitions I'm giving, but to give you a basic idea, this is what I feel distinguishes invasions from reductions.

Author:	Bantari [ Thu Mar 19, 2015 9:36 pm ]
Post subject:	Re: What is the difference between Reduction and Invasion?
DiogoBarbosa wrote: Hello, I was reading about Reduction and Invasion on the Sensei's Library. http://senseis.xmp.net/?Invasion and http://senseis.xmp.net/?Reduction But I did not understand the difference between them. Some people tried to explain to me in the OGS chat, but I have not found difference between the concepts yet. Please, Can anyone help me? Thank you a lot. On the simplest level, both techniques are means to make enemy areas smaller. The difference, conceptually, is as follows: 1) when you play reduction, your hope is to run away with reducing stone (connect to outside) 2) when you play invasion, your hope is to make life rather than escape. Or another way of putting it: 1) reduction limits the enemy area from the outside, while 2) invasion jumps right in and hopes for the best. Invasion, if it works, is a much more severe move. Reduction, on the other hand, is much safer. It often takes great skill and careful positional judgement to decide which path you should walk in any given position. But the difference is, in a nutshell, as I stated above. Some more knowledge: With reducing moves, what you often hope for is an answer - your opponent blocking any further way into his space. This move alone is usually a gain for you, and you might play tenuki satisfied that you made him make a defensive move and limited his points. But you need to be careful - when a reduction is too deep, he might instead block your escape route and you will have to fight. If you lose that fight, he would have usually gained more than if you did not try to reduce at all. So the 'depth' of the reducing - i.e. how far into his space you play - makes for a successful or failed reduction. The exact point has to be carefully considered. With invasions - there are also hard decisions to be made, although usually there is no doubt - you will get into a fight, and tenuki is usually very bad idea. The decisions about invasions are: at which exact point you need to invade to have the best chance of survival. Very important here are issues of shape and aji which you can exploit to give yourself a better chance. Often invasions need to be first prepared - moves on the outside need to be played first (usually sente moves) to create the aji which will allow your invasion to survive. Not to confuse you, but... Reality is usually much more complicated than that, and the result depends also on the plans and moves of your opponent as well. It often happens that reducing stones end up fighting for life and invading stones manage to escape or connect to outside. But sill, the basic distinction is as above: reduction limits from the outside while invasion jumps inside and tries to survive. Sometimes it can also happen that your invasion is actually a probe - you play an invading move to see how he answers, and then either continue with the invasion or play elsewhere depending on what he does. Sometimes such probe/invasion moves are just a preparation for a deeper reduction moves... All in all, this is an extremely complex issue, and as you get stronger you will learn more and more about the concepts.

Author: Bill Spight [ Thu Mar 19, 2015 9:42 pm ]

Post subject: Re: What is the difference between Reduction and Invasion?

To distinguish between an invasion and a reduction, if a play is below the 4th line, it is an invasion. For higher plays, a good rule of thumb is to draw a sector line between stones that frame the potential territory. If a play is below a sector line, it is usually considered an invasion. But maybe not. There is no hard and fast distinction between the two in all cases.

Click Here To Show Diagram Code: [go]$$Wc Standard reduction. $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . B . . . . 1 . B . . . . . O . . . | $$ | . . . , . . . . . , . . . . . . O . . | $$ | . . . X . . . . . X . . . . . X O . . | $$ | . . . . . . . . . . . . . . X . X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ --------------------------------------- $$ {LN C5 K5}[/go]

is a standard reduction of the Black framework. It lies on the sector line between the two :bc:

stones.

Click Here To Show Diagram Code: [go]$$Wc Standard reduction II. $$ | . . . , . . . . . . . . . . . . . . . | $$ | . . B . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . 1 . B . . . . . O . . . | $$ | . . . , . . . . . , . . . . . . O . . | $$ | . . . X . . . . . X . . . . . X O . . | $$ | . . . . . . . . . . . . . . X . X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ --------------------------------------- $$ {LN C9 K5}[/go]

Here

lies below the indicated sector line, but is still considered a reduction.

Click Here To Show Diagram Code: [go]$$Wc Reduction, maybe? $$ | . . . , . . . . . . . . . . . . . . . | $$ | . . B . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . . 1 . . . . . B . . . . . O . . . | $$ | . . . . . . . . . , . . . . . . O . . | $$ | . . . X . . . . . X . . . . . X O . . | $$ | . . . . . . . . . . . . . . X . X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ --------------------------------------- $$ {LN C9 K5} $$ {LN C6 K5} $$ {LN C6 K3} $$ {LN C9 K3}[/go]

A lot of people would regard this as a reduction, even though it is within four sector lines. But I think that others would consider it an invasion.

Click Here To Show Diagram Code: [go]$$Wc Invasion, maybe? $$ | . . . , . . . . . . . . . . . . . . . | $$ | . . B . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . . . . . . . . O . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ | . . X . . . . . . . . . . . . . . . . | $$ | . . . . . . . . . B . . . . . O . . . | $$ | . . . 1 . . . . . , . . . . . . O . . | $$ | . . . X . . . . . X . . . . . X O . . | $$ | . . . . . . . . . . . . . . X . X . . | $$ | . . . . . . . . . . . . . . . . . . . | $$ --------------------------------------- $$ {LN C9 K5} $$ {LN C6 K5} $$ {LN C6 K3} $$ {LN C9 K3}[/go]

I think that most people would call this an invasion, but some might still call it a reduction.

As far as ambiguous cases go, really, nobody much cares what you call them. :mrgreen:

Author:	Bill Spight [ Thu Mar 19, 2015 9:55 pm ]
Post subject:	Re: What is the difference between Reduction and Invasion?
Just to add to the purposes of reductions and invasions, sometimes a reduction or invasion may be sacrificed, although invasions are more likely to be sacrificed than reductions. Often a reduction is chosen over an invasion in order to keep sente after the opponent protects against a further incursion. Sometimes the opponent wants to take sente himself, and does not protect, so that a reduction leads to a later invasion. And sometimes a reduction will threaten more than one invasion, so that it sets up a later invasion, since the opponent cannot protect against them all.

Author:	RobertJasiek [ Thu Mar 19, 2015 10:22 pm ]
Post subject:	Re: What is the difference between Reduction and Invasion?
A _reduction_ reduces the opponent's eyespace, territory or moyo from the outside so that, if the opponent defends from the inside, the reduction (or a follow-up to the sacrificed initial reduction stones) must live on the outside, and if the opponent attacks from the outside, the reduction (or a follow-up to the sacrificed initial reduction stones) can live on the outside or become a reduction-or-invasion. An _invasion_ reduces the opponent's eyespace, territory or moyo from the inside so that, if the opponent defends from the outside or the invasion cannot move to the outside, the invasion (or a follow-up to the sacrificed initial invasion stones) must live on the inside. A _reduction-or-invasion_ reduces the opponent's eyespace, territory or moyo so that it depends on the opponent's choice whether it becomes a reduction or invasion. A _test invasion_ reduces the opponent's eyespace, territory or moyo from the inside so that it depends on the opponent's choice whether it becomes a reduction, invasion or sacrifice for the sake of a follow-up reduction. Ko threat play increases the definition fun. EDITS

Author:	Bantari [ Thu Mar 19, 2015 10:37 pm ]
Post subject:	Re: What is the difference between Reduction and Invasion?
RobertJasiek wrote: A _reduction_ reduces the opponent's eyespace, territory or moyo from the outside so that, if the opponent defends from the inside, the reduction (or a follow-up to the sacrificed initial reduction stones) must live on the outside, and if the opponent attacks from the outside, the reduction (or a follow-up to the sacrificed initial reduction stones) can live on the outside or become a reduction-or-invasion. An _invasion_ reduces the opponent's eyespace, territory or moyo from the inside so that, if the opponent defends from the outside or the invasion cannot move to the outside, the invasion (or a follow-up to the sacrificed initial invasion stones) must live on the inside. A _reduction-or-invasion_ reduces the opponent's eyespace, territory or moyo so that it depends on the opponent's choice whether it becomes a reduction or invasion. A _test invasion_ reduces the opponent's eyespace, territory or moyo from the inside so that it depends on the opponent's choice whether it becomes a reduction, invasion or sacrifice for the sake of a follow-up reduction. Ko threat play increases the definition fun. EDITS How do you define 'inside' and 'outside'?

Author:	RobertJasiek [ Fri Mar 20, 2015 2:11 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
Inside / outside or internal / external is, for the general application case as needed for invasions and reductions, an open research question. However, until they are defined, the following definition is good enough: 'Neither' is the intersections of the alive stones. 'Internal' is 0- or 1-territory. 'External' is everything else.

Author:	oca [ Fri Mar 20, 2015 2:35 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
to me, the most difficult aspect is still to choose if (and when...) I should start an invasion/reduction or if I should just make a bigger territory / moyo. The problem with the invasion/reduction is that it often (always?) lead to a new "weak" group that I then need to deal with... but that's also really part of the fun... and maybe that's one problem too as I tend to invade when that's not reasonable just because I like to fight

Author:	Bantari [ Fri Mar 20, 2015 2:45 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
RobertJasiek wrote: Inside / outside or internal / external is, for the general application case as needed for invasions and reductions, an open research question. However, until they are defined, the following definition is good enough: 'Neither' is the intersections of the alive stones. 'Internal' is 0- or 1-territory. 'External' is everything else. What is '0-territory' and '1-territory'? (And what is 'alive'?) Ok, the 2nd question is a joke, just to point out that if if you wish to be precise, be so. But the 1st question is for reals.

Author:	RobertJasiek [ Fri Mar 20, 2015 3:28 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
http://senseis.xmp.net/?NTerritory

Author:	skydyr [ Fri Mar 20, 2015 8:51 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
I would add that reductions are usually sente, and invasions usually end in gote. Bill's rules above are also quite good, but it's also possible to reduce on, say, the second line when you have a secure attachment to a group on the side, like the well-known monkey jump. I think as a general rule, invasions expect to live locally or have a running fight, while reductions expect to make shape on the outside or connect to a living group, if the opponent fights as severely as possible. Of course, the opposite may happen if the opponent judges that the end result is better for them. Another way to think of it is that reductions seek to nibble at the edges, saying "your plan was reasonable, so I will limit it as much as possible" while invasions strike at the core, saying "you're claiming too much too loosely, so I will prove it by taking away the center of your moyo." One semi-proverb is that an invasion should be in an open space of at least 21 points to have a good chance, and another is that an invasion should have at least 3 good follow-ups (say, slide left, extend right, or jump into the center) to be viable. If it's not, then a reducing move is called for instead. Reducing moves on the outside also tend to have more of a global impact, since you might build thickness that will affect a fight on the other side of the board. On the other hand, an invasion is locally focused and ideally timed so that the thickness your opponent builds will not have as much of an effect on the rest of the game as the number of points you stole from their area.

Author:	i3ullseye [ Fri Mar 20, 2015 9:15 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
This is actually a pretty great question, and it looks like people are giving answers coming from different levels. Different interpretations of the words even in regards to the game. I always think there is a fusion here.... some actions are neither purely an invasion or a reduction, but a mix of both. But for me, Reduction is deciding how much you are giving your opponent in territory, and invasion is deciding how much you want to try to take from your opponent that they otherwise might have gotten.

Author:	Bill Spight [ Fri Mar 20, 2015 9:43 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
oca wrote: The problem with the invasion/reduction is that it often (always?) lead to a new "weak" group that I then need to deal with... but that's also really part of the fun... and maybe that's one problem too as I tend to invade when that's not reasonable just because I like to fight The question of a weak group is why you need to think about sacrificing an invasion, or even a reduction. You also need to think about greed.

Author:	Bill Spight [ Fri Mar 20, 2015 9:49 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
skydyr wrote: Bill's rules above are also quite good, but it's also possible to reduce on, say, the second line when you have a secure attachment to a group on the side, like the well-known monkey jump. When I was coming along, such moves were called neither reductions nor invasions, but yose. But language changes with time, and maybe in the future they will be called reductions.

Author:	Boidhre [ Fri Mar 20, 2015 10:32 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
skydyr wrote: One semi-proverb is that an invasion should be in an open space of at least 21 points to have a good chance I've only seen that proverb used to refer to situations where your opponent can cut off your access to the centre in one move.

Author:	John Fairbairn [ Fri Mar 20, 2015 10:51 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
There is a lot of after-the-fact interpretation going on here: people hear the words 'invasion' and 'reduction', take the English senses as the starting point, then superimpose their own notions of these concepts. Which may well work, but it has little to do with the original Japanese, and we may suppose they know a little bit more about go. Uchikomi itself has no sense that is even remotely normally translated as 'invasion'. It's basic meaning is simply 'driving in' [a wedge] and extended senses of this include pumping someone full of bullets, or peppering a position with shells. In go-lexicon definitions three ideas tend to be stressed: (1) you are hitting a definite vital point - this is a sine qua non given the term uchikomi; (2) you are 'encroaching' (侵入) on the opponent's territory, territorial framework, moyo or sphere of influence (i.e. not just territory); (3) the end result is either destruction of the opponent's area or 'invasion', i.e. 侵略 occupation = living inside. In other words, the Japanese player starts at a higher conceptual level than invasion, and actual invasion becomes just one option. Keshi similarly does not mean 'reduction'. The base idea is cancelling, extinguishing, erasing, turning off, or - in go terms - neutralising, and again what you are neutralising is not just territory but also moyos and influence. There is a term kezuru which uses the same kanji, and when used in go (not all that often) it displays its base meanings of paring down, whittling down, shaving, etc. This can be the effect of a keshi move, but yet again the Japanese player is starting at a higher conceptual level than reduction, and - again - actual reduction becomes just one option. Even if, in practice, the invasion/reduction options tend to dominate, I think it is useful for stronger players to try to acquire a feel for the more nuanced original meanings, at least when reading commentaries translated from Japanese. After all the idea is to understand the pro players' intentions. Keeping the Japanese origins in mind also demolishes notions such as monkey jumps being (Japanese-style) keshi reductions (though a monkey jump can also be described with the word 'encroaching' (侵入).

Author:	Bill Spight [ Fri Mar 20, 2015 11:08 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
skydyr wrote: One semi-proverb is that an invasion should be in an open space of at least 21 points to have a good chance, and another is that an invasion should have at least 3 good follow-ups (say, slide left, extend right, or jump into the center) to be viable. If it's not, then a reducing move is called for instead.

Author:	RobertJasiek [ Fri Mar 20, 2015 11:14 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
While OC Japanese players start from a higher conceptual level, non-Japanese players also start from a higher conceptual level but might express the high levels by different terminologies possibly not so closely related to the words invasion and reduction.

Author:	Uberdude [ Fri Mar 20, 2015 11:30 am ]
Post subject:	Re: What is the difference between Reduction and Invasion?
I remember move 48 I played here being rather interesting on the border between invasion and reduction. It's somewhat of a probe: if black answered below (at L7) then it would be a reduction and I would play further safe reductions (or yose moves if you prefer) from f2 and n2 (or try o4). But If black capped as he did in the game then I would invade and that initial stone becomes a good exchange that gives my invading group more space.

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