The following cmavo are discussed in this section:

Lojban questions are not at all like English questions. There are two basic types: truth questions, of the form “Is it true that ...”, and fill-in-the-blank questions. Truth questions are marked by preceding the bridi, or following any part of it specifically questioned, with the cmavo xu (of selma'o UI):

(Since the Lojban is tenseless, either colloquial translation might be correct.) Truth questions are further discussed in Section 15.8.

Fill-in-the-blank questions have a cmavo representing some Lojban word or phrase which is not known to the questioner, and which the answerer is to supply. There are a variety of cmavo belonging to different selma'o which provide different kinds of blanks.

Where a sumti is not known, a question may be formed with ma (of selma'o KOhA), which is a kind of pro-sumti:

Of course, the ma need not be in the x1 place:

The answer is a simple sumti:

A sumti, then, is a legal utterance, although it does not by itself constitute a bridi – it does not claim anything, but merely completes the open-ended claim of the previous bridi.

There can be two ma cmavo in a single question:

and the answer would be two sumti, which are meant to fill in the two ma cmavo in order:

An even more complex example, depending on the non-logical connective fa'u (of selma'o JOI), which is like the English “and ... respectively”:

An answer might be

(Note: A mechanical substitution of Example 19.20 into Example 19.19 produces an ungrammatical result, because * ... le zarci fa'u le briju is ungrammatical Lojban: the first le zarci has to be closed with its proper terminator ku, for reasons explained in Section 14.14. This effect is not important: Lojban behaves as if all elided terminators have been supplied in both question and answer before inserting the latter into the former. The exchange is grammatical if question and answer are each separately grammatical.)

Questions to be answered with a selbri are expressed with mo of selma'o GOhA, which is a kind of pro-bridi:

Here the answerer is to supply some predicate which is true of Lojban. Such questions are extremely open-ended, due to the enormous range of possible predicate answers. The answer might be just a selbri, or might be a full bridi, in which case the sumti in the answer override those provided by the questioner. To limit the range of a mo question, make it part of a tanru.

Questions about numbers are expressed with xo of selma'o PA:

The answer would be a simple number, another kind of non-bridi utterance:

Fill-in-the-blank questions may also be asked about: logical connectives (using cmavo ji of A, ge'i of GA, gi'i of GIhA, gu'i of GUhA, or je'i of JA, and receiving an ek, gihek, ijek, or ijoik as an answer) – see Section 14.13; attitudes (using pei of UI, and receiving an attitudinal as an answer) – see Section 13.10; place structures (using fi'a of FA, and receiving a cmavo of FA as an answer) – see Section 9.3; tenses and modals (using cu'e of CUhE, and receiving any tense or BAI cmavo as an answer) – see Section 9.6 and Chapter 10.

Questions can be marked by placing pau (of selma'o UI) before the question bridi. See Section 13.13 for details.

The full list of non-bridi utterances suitable as answers to questions is:

At the beginning of a text, the following non-bridi are also permitted:

Where not needed for the expression of answers, most of these are made grammatical for pragmatic reasons: people will say them in conversation, and there is no reason to rule them out as ungrammatical merely because most of them are vague.