Often we wish to talk about things other than the speaker, the listener and things we can point to. Let's say I want to talk about a talker other than mi. What I want to talk about would naturally fit into the first place of tavla. Lojban, it turns out, has an operator that pulls this first place out of a selbri and converts it to a sumti called a “description sumti”. The description sumti le tavla ku means “the talker”, and may be used wherever any sumti may be used.
For example,
means the same as
where “the talker” is presumably someone other than me, though not necessarily.
Similarly le sutra tavla ku is “the fast talker”, and le sutra te tavla ku is “the fast subject of talk” or “the subject of fast talk”. Which of these related meanings is understood will depend on the context in which the expression is used. The most plausible interpretation within the context will generally be assumed by a listener to be the intended one.
In many cases the word ku may be omitted. In particular, it is never necessary in a description at the end of a sentence, so:
means exactly the same thing as Example 2.38.
There is a problem when we want to say “The fast one is talking.” The “obvious” translation le sutra tavla turns out to mean “the fast talker”, and has no selbri at all. To solve this problem we can use the word cu, which so far has always been optional, in front of the selbri.
The word cu has no meaning, and exists only to mark the beginning of the selbri within the bridi, separating it from a previous sumti. It comes before any other part of the selbri, including other cmavo like se or te. Thus:
Consider the following more complex example, with two description sumti.
The sumti le vecnu contains the selbri vecnu, which has the “seller” in the x1 place, and uses it in this sentence to describe a particular “seller” that the speaker has in mind (one that he or she probably expects the listener will also know about). Similarly, the speaker has a particular blue-green thing in mind, which is described using le to mark blari'o, a selbri whose first sumti is something blue-green.
It is safe to omit both occurrences of ku in Example 2.45, and it is also safe to omit the cu.