Life In 19x19

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 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.

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.

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 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.

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.

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

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'?

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.

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

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.

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.

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.

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.

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.