Chapter 3. Diagrammed Summary of Lojban Grammar

Table of Contents
The Lojban sentence structure
The Basic Components (sumti and selbri)
Complex sumti
Attachments to sumti, selbri and sentences
Logical Connectives
Brief glossary of Lojban words used in these examples
xracartu torvelski be le lojbo gerna

This chapter gives diagrammed examples of basic Lojban sentence structures. The most general pattern is covered first, followed by successive variations on the basic components of the Lojban sentence. There are many more capabilities not covered in these examples. A Lojban glossary will be found at the end of this section.

The Lojban sentence structure

A Lojban sentence expresses a relationship (bridi), normally claiming that the relationship holds (that it is 'true'). A bridi relationship consists of several ideas or objects called arguments (sumti), which are related by a predicate relation (selbri). The following uses the Lojban terms bridi, sumti, and selbri, because it is best to come to understand them independent of the English associations of the corresponding words.

Some words used as sumti


I/me/my, we/us/our




this/this-here/this one, these/these here/these ones


that/that-there/that one, those/those ones


that yonder, those yonder


unspecified value (used when a sumti is unimportant or obvious)

sumti are not specific as to number (singular or plural), nor gender (masculine/feminine/neuter). Such distinctions can be optionally added.

Names may be expressed as sumti, labelled with la:

la meris. 

the one/ones named Mary

la djan. 

the one/ones named John

(Other Lojban spelling variations are possible for names imported from other languages.)

Some words used to indicate selbri relations


x1 (seller) sells x2 (goods) to x3 (buyer) for x4 (price)


x1 (talker) talks to x2 (audience) about x3 (topic) in language x4


x1 (object/light source) is blue-green


x1 (object/idea) is beautiful to x2 (observer) by standard x3

We will describe these and other possible sumti and selbri in more detail below.


The following conventions will be used to show the structure of Lojban sentences in diagrams:

  • The selbri relation will be italicized.

  • The sumti arguments will be underlined.

  • Optional separator/terminator words are placed in square brackets. They may be omitted if so bracketed. The general rule is that these may be omitted if and only if no grammatical ambiguity results. Each such word serves as an end marker for particular structures, making the overall structure of the sentence clear.

  • The structure of Lojban phrases is indicated by bars beneath the text, joining related words together.

  • Words modifying other words are indicated by arrows pointing from the modifier to the modified.

Basic structure of a Lojban sentence

sumti sumti ... sumti [cu] selbri sumti sumti ... sumti [vau]

  • Normally, there must be at least one sumti before the selbri.

  • Each selbri relation has a specifically defined place structure that defines the role of each sumti in the bridi relationship, based on its position in order. In the examples above, that order was expressed by labelling the positions x1, x2, x3, and x4.

  • cu acts as a separator after at least one preceding sumti to clearly mark the selbri. As the diagram indicates, it may often be omitted. There will be examples of this below.

  • vau goes at the end of the sentence, indicating that no more sumti will follow. It usually may be omitted.

Sentence examples

seller-x1 sellsgoods-sold-x2buyer-x3
I sellthisto that
for some price.(No more sumti)
I sell this-thing/these-things to that-buyer/those-buyers. (The price is obvious or unimportant.)

  • Both the cu and the vau are optional in this example and could be omitted

  • When an unspecified sumti (zo'e) is at the end of a sentence, it may be omitted.

  • Normally, there will be one sumti (the x1) before the selbri. There may be more than one:

seller-x1goods-sold-x2 sellsbuyer-x3
Ithis sellto that.
(No more sumti)
Translates as stilted or poetic English: I, this thing, do sell to that buyer.

Usually, more than one sumti will be placed before the selbri for style or for emphasis on the sumti displaced from their normal position. (Native speakers of languages other than English may prefer such orders.)


If there is no sumti before the selbri, then it is understood that the x1 sumti value is equivalent to zo'e; i.e. it is unimportant or obvious, and therefore omitted. Any sumti after the selbri start counting from x2, x3, x4...:

object/idea-x1 is-beautiful(to someone by some standard)
That/Those is/are beautiful. 
That is beautiful. (or) Those are beautiful.

When the x1 is omitted:

(Unspecified)is-beautiful(to someone by some standard)
Beautiful! (or) It's beautiful!

(Unspecified)sellsthisto that. 
(Look!) Someone's selling this to that!

Omitting the x1 adds emphasis to the selbri relation, which has become first and foremost in the sentence. This kind of sentence is termed an observative, because it is usually stated by someone when they first observe or take note of the relation, and wish to quickly communicate it to someone else. Commonly understood English observatives include Smoke! upon seeing smoke or smelling the odor, or Car! to a person crossing the street who might be in danger. Any Lojban selbri can be an observative if no sumti appear before the selbri.

cu does not occur in an observative; cu is a separator, and there must be a sumti before the selbri that needs to be kept separate, for it to be used. With no sumti preceding the selbri, cu is not permitted.

True/false (yes/no) questions (the word xu)

xu question sentence (Is-it-true-that...):

Is-it-true?I sellthisthat. 
Is it true that I sell this to that?

xu has a very unrestricted grammar, and is permitted virtually anywhere in a sentence. At the beginning of the sentence, xu asks about the truth of the bridi relationship. Elsewhere, in a sentence, xu attaches to the immediately preceding word (or the structure implied by that preceding word, when it is the marker for a structure). Thus, also after the vau ending the sentence, xu would ask about the entire bridi (the vau cannot be omitted if xu is to appear 'after' it).

xu appearing after a sumti questions whether the bridi relationship expressed by the sentence is true for that sumti value in particular:

I sellthisIs-it-true?that. 
Is it true that I sell this (as opposed to something else) to that?

Similarly, xu following vecnu in the above example would question the truth of the bridi relationship by specifically asking whether 'sell' is a true relation between the sumti.

We will discuss how to answer a xu true/false question below in the section on selbri.

Varying sumti order

There are ways to vary the order of sumti from the numerical order specified by the place structure. A sumti may be placed out of numerical order by labelling it in front with a tag indicating the actual numerical position of the sumti in the place structure. The structure is thus of the form FA sumti (where the FA category word shows which of the existing sumti places is being used, by number):

fa '1st sumti: x1'
fe '2nd sumti: x2'
fi '3rd sumti: x3'
fo '4th sumti: x4'
fu '5th sumti: x5'

One reason for using these tags is to skip a place structure place without having to insert a zo'e for each skipped place:

mi[cu]tavlafola lojban.
talker talkx4=language 
I talkin languageLojban.
I talk in Lojban (to someone about some topic).

which is equivalent to:

talker talkaudiencetopic
I talkto unspecifiedabout unspecified
la lojban.[vau]
in Lojban.
I talk in Lojban (to someone about some topic).

After a FA tag sets the place number, any later sumti places continue the numbering consecutively:

mi[cu]tavlafitala lojban.
talker talkx3=topiclanguage-x4
I talkabout thatin-language Lojban.
I talk about that in Lojban (to someone unspecified).

Another reason to use FA tags is to change emphasis; listeners focus most closely on the sumti at the beginning of a sentence.

fila lojban.[cu]tavlafamido
x3=topic talkx1=talkeraudience-x2
About Lojban talkIto you.
It's Lojban that I talk to you about (in an unspecified language).

There are other ways of rearranging the sumti of a sentence that will be discussed below.

Note that in all examples where a sumti is omitted, there is an unspoken and unspecified value for each of the omitted place structure places.

An observative can be formed by using fa to move the first (x1) sumti to the position after the selbri.

melbifa ti[vau]
Beautifulthis-is(to someone by some standard).
Beautiful, it is!

Basic structure of an utterance

People usually don't say just one sentence. Lojban has a specific structure for talk or writing that is longer than one sentence. The entirety of a given speech event or written text is called an utterance.

sentence .i sentence .i sentence [...] .i sentence
ni'o sentence .i sentence .i sentence .i sentence [...] .i sentence
ni'o sentence .i sentence [...] .i sentence

  • ni'o separates paragraphs (covering different topics of discussion). In a long text or utterance, the topical structure of the text may be indicated by multiple ni'os, with perhaps ni'oni'oni'o used to indicate a chapter, ni'oni'o to indicate a section, and a single ni'o to indicate a subtopic corresponding to a single English paragraph.

  • .i separates sentences. .i is sometimes compounded with words that modify the exact meaning (the semantics) of the sentence within the utterance. xu, discussed above, is one such word -- it turns the sentence from a statement to a question of truth. When more than one person is talking, a new speaker will usually omit the .i even though she/he may be continuing on the same topic. It is still OK for a new speaker to say the .i before continuing; indeed it is encouraged for maximum clarity (since it is possible the second speaker might merely be adding words onto the end of the first speaker's sentence). A good translation for .i is the and used in run-on sentences when people are talking informally: "I did this, and then I did that, and ..., and ...".

  • fa'o is an optional end-of-utterance marker, used primarily in computer input. It is not needed in human speech.

You may now see why the vau at the end of the sentence can generally be omitted. Since the following word will usually be an .i or a ni'o starting a new sentence or paragraph, there is no possibility of ambiguity if it is omitted. These separators prevent the sumti at the beginning of the next sentence from being mistaken as a trailing sumti of this sentence.


Lojban has no mandatory punctuation marks. Because Lojban speech exactly matches the written text representing that speech, all 'punctuation' that is used in English to show sentence structure, questions, exclamations or tone of voice, and even quotations must be expressed in Lojban as actual words.

The special use of the apostrophe, period, capitalization and commas is outlined in Overview of Lojban Grammar.

Tip: Some optional conventions allow certain punctuation symbols to appear to clarify printed text, making it easier to read. (Such punctuation is not considered part of the standard Lojban orthography, and is not accepted by all Lojbanists.) These punctuation symbols always appear in conjunction with the printed word representing that punctuation symbol, rather than replacing it. Thus a xu question may be marked with a question mark immediately after the xu (or immediately before the xu, possibly inverted, as in Spanish). Other questions may similarly be marked with a question mark after the word indicating the question -- not at the end of the sentence. There are words that may be associated with exclamation points, start of quotation (represented by <<) and end of quotation (>>). For example:

.i xu? do klama
.i ?xu do bacru <<lu mi klama li'u>> bau la lojban.
.i ?xu .ue! do bacru <<lu do bacru <<lu mi klama li'u>> bau la lojban. li'u>>