Go is unusually permissive. There are no pieces that move in special ways, no squares that are off limits, no pieces that can only go forward. You may place a stone on any empty intersection — with just two exceptions. Understanding those exceptions is not only about avoiding error messages; it is the foundation for understanding eyes, and eyes are what keep groups alive.
Exception 1: suicide
You may not place a stone where it, or the group it joins, would have no liberties after the move — unless the move captures enemy stones.
Picture an empty point completely surrounded by white stones, with no black stone next to it. If Black plays there and the move captures nothing, the new black stone has zero liberties. That is suicide, and it is illegal on this site and in most rule sets.
The same applies to groups. If you add a stone that connects to one of your groups and the resulting larger group has no liberties left, the move is suicide.
When a "suicide-looking" move is legal
The important exception: if your move takes the last liberty of an enemy group, the enemy stones are removed first. Your stone then has liberties where the captured stones were. The move is a capture, not a suicide.
Exception 2: repeating a position (ko)
The second illegal move is one that recreates a board position that has already occurred. In practice this is the ko rule: after a single-stone capture that could be answered by an immediate single-stone recapture, the recapture must wait one move. The version used here, positional superko, forbids any whole-board repetition. The details are in the ko rule.
Why suicide matters: eyes
Here is where the suicide rule becomes strategy. Imagine a black group that completely surrounds an empty point. White cannot play inside that point, because the white stone would have no liberties — unless that single point is the black group's last liberty, in which case the move captures.
Now imagine the black group surrounds two separate empty points. White can never fill both at once. Playing in either one is suicide while the other is still empty, because neither move takes the group's last liberty. So the black group can never be captured. It is permanently alive.
Those enclosed empty points are called eyes, and "two eyes live" is the most important principle of life and death. It is a direct consequence of the suicide rule. Read two eyes to live for how to build them.
A small example on the edge
Count it for yourself: the black stones a2, b2, c2, d2, b1 and d1 form one connected group. Its only liberties are a1 and c1. A white stone at a1 would have no liberties and would not capture anything, because the black group still breathes at c1. The same is true in reverse. The group can never be captured.
Illegal moves that are not really moves
A few things feel like rule questions but are not:
- Playing on an occupied point is simply impossible; a point holds one stone.
- Moving a stone does not exist in Go.
- Passing is always legal. You may pass even when legal moves remain.
Rule variations you may hear about
Some rule sets, notably the New Zealand rules, allow suicide of a group of more than one stone. It is almost never a good move even where it is allowed, and on this site it is not allowed, so you can ignore it.
Practical tips
- If the site refuses your move, check two things: does your stone have any liberty after the move, and does the move bring back a previous position?
- When your opponent's group surrounds a single point, you cannot play inside unless it captures. Look for ways to stop them making a second eye instead.
- When your own group encloses one empty point, you are not yet safe. Try to make a second, separate eye.
Try the ideas out against the computer on the home page. Build a group on the edge that encloses two points and watch the computer fail to capture it; then try a group with only one enclosed point and see what happens.
One eye is not enough
It is worth looking at what happens when a group has only one enclosed point. Suppose White has surrounded a black group from the outside, and the black group encloses a single empty point. At first White cannot play inside, because that point is not yet the group's last liberty — the group still has liberties on the outside. But White can fill the outside liberties one by one. Once all of them are gone, the enclosed point becomes the last liberty. Now White plays inside, and the move is a capture, not suicide.
So a group with one eye can always be captured eventually, provided the outside liberties can be filled. A group with two separate eyes cannot, because at the end the two eyes are still two liberties, and a stone placed in either is suicide.
A common beginner surprise
Beginners are often surprised when the computer plays a stone right into the middle of their "territory" and the site accepts it. The reason is always the same: the point was not surrounded, or it was the last liberty of a group. If the computer's stone captures your group, your territory was really one eye, not two. Next time, make the second eye earlier.
Why the rule exists at all
Without a ban on suicide, players could fill their own eyes or create strange positions where stones disappear by their own move. Most rule sets simply forbid it, which keeps the game clean: every stone placed stays on the board until the opponent captures it.
Frequently asked questions
Is suicide ever allowed on this site?
No. A move that leaves your own stone or group without liberties is illegal, unless it captures enemy stones first.
Why can my opponent play inside my group's enclosed point?
Because that point is your group's last liberty, so the move captures your group. Make sure your group has a second, separate eye.
What is the difference between suicide and capture?
If a move takes the last liberty of an enemy group, the enemy group is removed and your stone survives: that is a capture. If it takes your own last liberty without capturing, it is suicide.
Can I always pass?
Yes. Passing is legal at any time. Two passes in a row end the game.
Do these rules differ between countries?
The core rules are the same everywhere. Differences are mostly about scoring and the exact wording of the repetition rule.
