Lately I've played too many games where I get overly defensive and suddenly I find my opponent has started snatching huge chunks of the board. Often I'd like to invade his territory, but that's when it gets tricky. I know about the 3-3 invasion in the opening and if there are few stones on the board then it's usually easy to see where to grab some territory. When the board fills up too it's usually clear to see where any invasion is just going to fail miserably. But between those extremes there are times when I often think I might get away with an invading stone.

Currently I'm using the Many Faces Of Go program. A helpful feature is that you ask for advice on potential moves according to criteria you set. So if you want to know where a good place to start an invasion is you can ask, and it will display an "I" symbol on the board. However many times I've done that and then the program places another stone close by and tells me that my stone is dead!

So are there any guidelines you can follow about when an invasion might work? Or is it mostly intuitive?

Hi cel70,

Usually, "generalized" (cosmic) questions like that come from adults (beginners).
Children usually don't ask questions like that (in Go) --
they just play hundreds and thousands of games,
and thanks to their amazing brains, they can remember many shapes, tesujis, etc.

We can come up with very general (vague) guidelines,
but at the end of the day, we must look at a particular board.

Example: if you're already behind, and if you just play "peacefully," you'll probably lose; in that case, you must try something, like an invasion -- you have no choice anyway.

Examples of more vague, general guidelines:
- the bigger the space you're invading, the easier (more likely to succeed).
- the more ways you can "escape," the better.
- the more weaknesses in your enemy's shapes, the better.
- the stronger your nearby friendly stones, the better.
- the more tesujis in your toolbox, the better.
- the more knowledge of (common and uncommon) shapes, the better.
- the better you can read, the better.

In a way, that's all common sense.
But what to do exactly on your particular board ?
A thousand guidelines cannot help you.
Because even a single stone can make a huge difference.
And the exceptions are practically infinite.

The concept seems intimidating, but in way I'm pleased. It means that aspect of Go isn't merely a mathematical exercise.

It's a hard topic. You should share some games and get feedback.

It's also possible you're invading too late: you mention playing too defensively. With every move or gote sequence you make, you should think "how can my opponent reinforce/expand their moyo. Do I have a way of coping if they do?" Usually there's a tradeoff between taking territory and letting your opponent grow their moyo. But there's a tipping point where the next move solidifies the moyo to the extent that an invasion is too hard. It's critical to anticipate that tipping point and make your move before it happens, even if it means giving up a nice move elsewhere.

_________________
Occupy Babel!

One can invade an opponent's territory, and one can reduce it.

Here is a pro game that shows two common invasions, and a play that could be called an invasion or a reduction. It also shows an endgame invasion.

Very important. Note that the last two of these moves were played with the intention of sacrificing them. An invasion does not have to live to be successful.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Some examples of normal invasions and extensions.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

Another game, with a number of invasions, reducing plays, and plays on the frontier of frameworks.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

For the beginner, the answer is: you know that the invasion is necessary, is advantageous or fair, and the important stones of the invasion group live. If a necessary invasion is too complicated for you, probably it means that you missed your chances to reduce or invade earlier.

You are mostly asking about how to defend the invasion stone, I think. And a key concept is miai, in the form "give yourself two options". For example, 3-3 invasion of the 4-4 point: you plan 3-4 or 4-3 next.

This type of pattern underlies many types of defensive play. You want to be able to continue at A or B next; and from A you want to have options C or D, from B options E or F ...

This may seem like extensive reading; but I think positions that are "porous" in this way for the defender are something you can see by intuition, when the situation is only partially enclosed.