What is the difference between Reduction and Invasion?

[Boidhre]

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.

[John Fairbairn]

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).

[Bill Spight]

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.

[RobertJasiek]

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.

[Uberdude]

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.

[Bill Spight]

Nice play.

I'd be interested in your views about a somewhat different play at that point.

[oca]

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.

Wow... If one day I can play at 1/10 of that level, I Will allready be very happy... btw, I'm surprised That black approached your 3-3 stone that early...

[Bantari]

http://senseis.xmp.net/?NTerritory

Do you think such levels of abstraction are appropriate for beginenrs?

[Uberdude]

Bill, what is the purpose of playing to the right a bit? Are you eyeing up the q7 weakness? Or aiming at q10? That could work well with something on the right side, or even some attacking potential if white could also get L4 but probably white won't have a rhythm to get both of those. I considered moves around the one I played, but not that far right. My move had a very nice feeling and worked well with my planned h4/l4 continuation if black capped. It's hard to know how to answer as black in either case, but if black follows my idea of shrugging his shoulders and abandoning the moyo to make some cash at r15 what does white do next (and how different to with L9)? I can see that your move is easier to run away to the north west if black caps, but I actually wanted black to cap my move because then I live inside and turn the cap to dame.