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Shape is one of the very fundamental concepts of Go - and yet it is one which is the most difficult to explain. I mean - shape by itself is easy to explain - it is the pattern the stones form on the board! It usually refers to a group of stones, or a bunch of stones (which are loosely connected) and not to the over-all pattern of all the stones on the board.
The thing which is hard to explain is which shape is considered good and which is considered bad and why. Basically - it is an issue of taste - which is acquired with experience. More experienced players have a batter developed taste then weaker players - and this taste guides them through the maze of shape, so to say, and helps them determine which shape is good and which is not.
A strong player can look at a shape and tell you if he thinks the shape is good or bad, but when you ask him why, chances are he will have hard time answering. The answers I usually get are of the type "It is not efficient" or "It has a weakness" or "It is too vulnerable" - which all give an indication about good shape, but does not really mean all that much! When I ask why a shape is not efficient I often hear the its because it has "Bad shape" - which completes the circular argument, hehe....
Now it is my turn to try to come up with an explanation of good and bad shape - and I already know that whatever I say will not be adequate. Yet I will try, and I hope that you will get at least a little glimpse at what shape is all about.
To start, lets think about good shape - and then, once we understand what it is, we will call everything else a bad shape, ok? Sounds simple.
Ok - first - what is an ideal shape? Well - think of all the ideal characteristics a pattern (or group) of stones can have - it is strong (no weaknesses), it exerts strong influence across the area, and it surrounds a lot of territory. It also has a very good prospects of making two eyes (and thus being unconditionally alive - more about it here) or even having two eyes already! At the same time, it attacks enemy stones and prevents them from making two eyes, and spreading out, and exerting influence, and surrounding territory! In other words - a perfect group of stones, hehe.... Can you imagine it?
Well - of course you cannot imagine it. Such a group does not exist, or at least I do not think so. But here we come to the idea of a good shape - its a shape that has some of the features attributed to the perfect shape - not all of them but some of them, or maybe all of them but just to some extent. A good shape is the real-life representation of perfect shape. And, of course, the close the shape to the ideal, the better!
I think that the most important attributes of good shape is that it is hard to cut by the opponent and it is hard to attack and kill.
A good shape is a shape which is light - which has lots of potential - for making eyes, for escaping, for attacking, or for surrounding areas. And good shape is good - its a shape you want your stones to have. And that's it, hehe...
Hope the above ranting gave you a good idea about good shape. Now to some practical considerations.
First of all - a good shape is one which is hard to kill, right? Now - you kill stones by taking their liberties away - so it seems reasonable that good shape is a shape which maximizes the liberties (explained here) - since the more liberties a shape has, the harder it is to kill. Look at the Position 1 of Fig 3-1 - it shows 2 black groups, each of them composed of 3 stones but having different shape. Which shape is better? Which shape is good? Well - first, count the liberties of each group. The group on the left (around 'a') has 8 liberties. The group on the right (around 'b') has 7 liberties! So here we go - the same 3 stones can have different amount of liberties depending on the shape they're in. A good shape will have more liberties, a bad shape - less. So the group on the left has a batter shape then the group on the right!
| Position 1 | Position 2 | Position 3 |
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Note:
The group on the
right in Position 1 of Fig 3-1 has a shape which is
called empty triangle - you can see why! It is often seen
in games of weak players (and often in my games too, hehe), but the pros
are going to great lengths to avoid making it. It is almost a
perfect example of bad shape - because it is so inefficient in terms of
liberties. Still - sometimes it cannot be avoided and even the
pros are forced to make it occasionally (about ranking and pros you can
read here).
Now, lets look at the shape in Position 2 of Fig 3-1. The half-bamboo connection (explained here) in this position is also composed of 3 stones - which also are connected together (or at least they are hard to be separated). But if you count their liberties - they have 9! Actually - they have 10 liberties, but one of them is shared between the single stone and the pair - so the enemy would just have to spend 9 stones to kill the group. Therefore - such shape is better than the shapes in Position 1!
Going back to our discussion of half-bamboo joint (see here) and why a bamboo connection is better than firm connection when threatened, you can now see that the a firm connection would reduce the black stones to 9 liberties (or even 8 liberties since one liberty would be taken by the white stone) while a bamboo-joint will ensure the group to have 10 liberties (actually - 12 liberties, but two of them are shared). Look at Position 3 of Fig 3-1 and count for yourself if you do not believe me. The easy-to-see reason why the firm-connected shape is bad is because it contains an empty triangle - which, as you already know, is very bad!
Another important trait of a good shape is that it must be easy to make two eyes. This also hangs together with the assumption that a good shape should be difficult to kill. Now - what kinds of shapes are easy to make eyes of? Simple - its easy to make eyes if all you have to do is to add one stone! So a good shape can have some points almost surrounded, it will have many walls and angles and crooks which you can use to make eyes with! But remember - empty triangles are bad, so the angles we need better not be firm empty triangles. A good substitute is the tiger-mouth connection (explained here) - and this is partially why it is so often used!
Lets look at Position 4 of Fig 3-2. Would it be easy for the black group to make eyes? Well - certainly! He can make one eye by playing at 'a' easily, or by playing at 'b' - note that 'c' is also an important eye-making point. And the rest of the group provides enough liberties to give black time to figure out where to make another eye long before white could manage to surround him! This is a good shape, this is a safe shape. This is a strong shape! Another example of a good shape is the marked black stones in Position 5 - here the important points for making eyes are 'a', 'b', and 'c'.
| Position 4 | Position 5 |
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Another, more complicated example is given in Position 6 of Fig 3-3. Here, black attacks the white marked stone with '1', white tries to run out with '2', and black blocks him with '3'. Now - white plays at '4' - and this is a bad shape - the empty triangle! Not good. But what should white do instead? Well - it is shown in Position 7. Instead of '4' in Position 6, white simply jumps lightly and attaches to the other black stone. And after black strengthens his solitary stone with '5' (black '5' can also be at 'a'), white makes the good shape move with '6' - and he is out from under the rain - and much better than in Position 6 too - white stones have good shape now! Position 8 shows what happens if black tries to separate the white stones instead of reinforcing with '5' in Position 7 - black loses some stones!
| Position 6 | Position 7 | Position 8 |
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Good shape is very important! A large part of the Go game is about how to make a good shape and how to prevent the opponent from making one! It is also about proving to the opponent that the shape he makes is bad - and you can do that by being aware what weaknesses a shape has and by choosing such moves that this weaknesses are exposed! Of course - the opponent will try doing the same to you - and so the merry dance begins! Go is great, but a lot of it is just a matter of opinion (or taste) - and its up to you which shapes you feel good about and which ones you feel bad about. And it is up to your opponents to prove how desperately wrong you are!
So much about good shape. For now. But how about a bad shape? Well - as the name indicates, a bad shape is bad and so should be avoided. But not always! Part of Go's beauty is that a player cannot really afford such narrow way of thinking! You should have your mind open and try to research all the possibilities - and sometimes it happens that a move which produces a bad shape is the best move!
Your aim in the game should be to find the best move (both in the game-theoretical sense and in psychological sense). If this best move makes bad shape - tough! Its still the best move and you just go right ahead and play it!! I saw many players disregarding good moves because they did not appeal to their sense of what is good shape. Such attitude is a mistake! Go is a great game, its a game which is alive - and as with all living creatures, most of it is beautiful, but some of it is ugly - and even in this ugliness there is beauty! To become a good player you have to know both sides of the path.