Ambiguous Position

An ambiguous position or endgame (position) or game (in a CGT context) is one that can not clearly be classified as sente or gote.^[1]
There are two cases, however: among the largest local options for at least one player there are either

• equally large sente and gote options or
• one or more ambiguous moves.

Note that “a position with an ambiguous move” is only one case of “an ambiguous position”.
Note also that the term “ambiguous” is itself ambiguous; in most cases it is preferable to use “ambiguous move” or “ambiguous position”, and to link to the appropriate page.

Type 1: Sente and Gote options

1.1 Either sente or gote?  

In this example^[2], Black has a 1 point gote (miai counting^[3]) with - , , or a one-point sente play with - .

It is not unusual to have both sente and gote options in a position, but we typically consider a position to be sente or gote according to the largest option. Here they are the same size, and the position is ambiguous. Black has the privilege of playing sente.

Type 2: Neither Sente nor Gote

Example 2.1: Ambiguous rescue

2.1 Ambiguous rescue  

This play is worth three points. If White saves one stone, there is another three point play left.

This isn't exactly sente, because White cannot normally make the play at a time when Black cannot afford to play here instead (White does not have the privilege). But it isn't exactly gote, either, because White will normally make the play when Black's reply will be the largest play on the board. It is an ambiguous move (for White).

So in other words, it is indeed sente for White, but not in the sense that Black cannot afford the reverse sente. ~srn347

Bill: Black does not have to reply locally, either. So it is not sente.

Robert Pauli:
With four copies of the situation above and White starting, it could either go
4 * 6 (Black treats as sente) or
0 + 6 + 9 + 9 (Black treats as gote):
24 in each case.
Is that what's behind?

Example 2.2: 2+UP

Robert Pauli:
Is below also sote? (2 + 2 + 2 + 2 = 0 + 2 + 3 + 3)
(I wasn't aware of UP at that time.)

2.2 2+UP  

Example 2.3: Two ambiguous options at once

2.3 Ambiguous hane — ambiguous descent  

Under Japanese rules, this region’s mast temperature is 1 but its mast is purple up to temperature 5. The descent leaves a 5-point simple gote, and the hane leaves a 5-point gote such that if the opponent plays it (crosscut) then a star is left. Since whoever plays first here gets the choice of what would result from their opponent playing next here, this region should presumably be played at temperature 5, which makes both descent and hane ambiguous moves.

Robert Pauli: Here’s my original contribution with what seems to me a less difficult rationale.

See also: Further discussion and examples

• Ambiguous Ko – A special sort of ambiguous position
• Multiples of Ambiguous Positions – Bill expands on an inaccuracy of his at Method of Multiples
• Tedomari/Discussion – Includes a question (here) by Jesusin about which one-point play to make. (Moved there from /Discussion here)
• One Thousand and One Life-and-Death Problems / Problem 593 discussion – Another ambiguous position (after )
  
• Ongoing Game 1 / Move 249 – Ambiguous after White's play.

Notes and discussion

[1] The original sentence was: "The Ongoing Game has a position that, with a couple of changes, is ambiguous whether it is sente or gote." If anybody knows why it starts with "ongoing game" and what was meant by "with a couple of changes" please clarify. I propose to delete this (and this footnote) - this is sufficiently expressed by Bill's footnote 2. BTW, I also set the difficulty from n.a. to "Intermediate" - please feel free to change. Also, I moved part of this to the /Discussion page. -- Sebastian

Bill: Hi, Sebastian. :-)

I intended ambiguous position to be a technical term with a more specific meaning than the new definition above. However, I did not want to give a formal definition, in line with my view that such definitions tend to be stumbling blocks for my intended audience of regular go players. I thought that examples, instead, were better for getting the idea across.

[2] Bill: The first example comes from Ongoing Game 1, with a couple of changes.

[3] About counting, see the discussion of Georg Mischler's question on /Discussion.