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As we said in our discussion of connections and groups, stones in Go are considered connected if they are vertically of horizontally adjacent, but not vertically! Technically, this is true, but there are methods of using diagonal moves to effectively (if not technically) connect groups of stones or at least to make it impossible for them to be cut.
The most common example of such "diagonal" connection is the hanging connection or the tiger's mouth as it is sometimes called. This "connection" is illustrated on Fig 1-1. It is important to understand that it is not really a connection per se - it just makes it impossible for the opponent to cut (for now).
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Let us look at Position 1 of Fig 1-1. Black has two groups of stones which white can separate by playing at 'a'. The sensible thing for black to do is to connect his stones. The straightforward thing to do would be to just play at 'a' and firmly connect black groups. But there is another way! Look at Position 2 - what if black plays at '1' there? Are his groups connected? Well - technically, when we look at the definition of connection (vertical or horizontal adjacedness) - the black stones are not connected! But maybe this was the wrong question to ask - lets ask ourselves this question instead: Can white cut the black groups apart? He can sure try, as shown in Position 3, by playing at '2' - but it does him no good, since black just kills the cutting white stone with '3'. Ok - so white cannot cut? Does that mean that black is connected? The answer is this: Technically black is not connected, but effectively he is! And it is the effectiveness of a connection that should concern us, not the technicality.
Here are some more examples of the tiger-mouth connection. In both position in Fig 1-2 'a'is in the tiger's mouth, and the stones around it create the hanging connection. Notice that in Position 4 the triangled white stones also form a tiger's mouth connection together with white stone at '2'.
| Position 4 | Position 5 |
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There are other hanging connections besides the tiger's mouth. They are even more vague and less firm, but they have their strengths and so they have their place in a Go-player's arsenal. One of such connections is shown in Position 1 of Fig 2-1. Instead of firmly connecting at 'a', black lightly jumps to '1'. "What!?" - you say - "this is a connection?? But its not even diagonal!!" Well - you are correct, it is not diagonal, and as with the tiger's mouth shape - technically it is not a connection at all. But, again as with the tiger's mouth, what counts that this move effectively prevents white from cutting at 'a'! What happens if white tries it anyways - you can see in Position 2: white stones get captured in a ladder (more on ladders here). The result, after killing the white stones (denoted as 'x's) can be seen in Position 3 - and it is obvious that white's attempt at a cut failed miserably! So now again - does black '1' in Position 1 connect the black stones or doesn't it? Hehe....
| Position 1 | Position 2 | Position 3 |
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Now let us look at yet another example of hanging (or indirect) connection. It is illustrated in Position 3 of Fig 2-2. It again starts with the same position as our previous examples, but now black chooses to connect n yet another way - with '1'. Is this an effective connection or isn't it? It is! - and what happens if white tries to cut at 'a' anyways is shown in Position 4 (or at least the first few moves of the ladder sequence - you may try to come up with the rest by yourself).
| Position 4 | Position 5 |
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The weakness of such hanging connections is the fact that they relay on the presence or absence of stones in other parts of the board (after reading about ladders here, you may try to imagine what would happen to the above connections if white decided to place a ladder-breaker somewhere in the path of a prospective ladder). This means that the player who connects in such way (in this case - black) has to be very careful and attentive to what happens on the rest of the board and how it affects the connections. A connection like '1' in Position 1 or the one in Position 4 may cease being a connection depending on the overall development of the game. So keep your eyes open and don't get caught napping!
Hanging connections are good, often better than firm connections, but they also have a weakness. This weakness is that it is possible for the opponent to peep the connection, i.e. to threaten to cut - and you have to answer this move or your stones will be cut. This gives the opponent one move "for free", so to say - since you have to answer by defending your connection.
In short, a peep is a move which threatens to cut an indirect connection.
Position 1 of Fig 3-1 illustrates such peep. White '1' threatens to cut the black groups by playing at 'a' next - white '1' is a peep, it looks right into the tiger's mouth! Position 2 shows what happens after the inevitable connection - white, who got the "extra" move at '1', can now extend to '3' thus "staking out" the left side as his prospective territory. Taking control of the left side was easy for white because of the peep at '1' in Position 1. Sometimes black tries to resist the peep - as, for example, he does in Position 3. This situation is a little better fro black than Position 2, but it still does not change the outcome very much - white still controls the left side (even though it seems smaller now than in Position 2) and black still had to waste a move to connect at '6'.
| Position 1 | Position 2 | Position 3 |
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Generally speaking, peep is any move that is directly threatening to cut through a loose connection. Some more examples are given in Fig 3-2. In each case, black '1' is a peep.
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Well, - after reading this page, you probably ask yourself "So, what is so good about the hanging connections? Isn't it better to just connect firmly?" This is a good question and the answer shows the depth of Go. Both hanging connections and the firm connections have their plusses and their minuses. The plus of the firm connection is obvious - it connects once and for all, and the owner of the stones does not have to worry about the connection being severed by a stone appearing in another part of the board. But hanging connections have their plusses too - they usually try to kill two birds with one stone - they give up some of the firmness in exchange for some influence in other directions. For example, look at Position 4 of Fig 2-2. Black '1' defends against the cut at 'a', but it also performs other functions - it denies white the upper left corner and attacks the single white stone in the lower left. As a comparison, imagine black connecting firmly at 'a' and the white playing the extension at '1' himself - the situation would be totally different, much better for white.
So here we are - with every move you make you have to weight out such pros and cons, decide between different ways to accomplish the same goal, each with its own strengths and weaknesses. Before placing a stone on the board, you are standing on a forked path, and its entirely up to you which road to choose. It is important to have an idea about what is going on in the game, and what kind of weaknesses you can afford. If you make the wrong choice, a skillful opponent can use it to his advantage and that might cost you the game. On the other hand - if you choose right, you might just be making the winning move. Sometimes a firm connection is best, sometimes a hanging one is better. And out of different kinds of hanging connections, some might be bad, and some might be good - depending on position. Confusing, eh? Don't worry - to decide issues like this all you need is experience and this is easily acquired by playing a lot of games! Just enjoy playing Go, and the strength will come by itself in due time.