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The grammar of Lojban is based on predicate logic. The majority of the grammar is borrowed from the prior "logical language" Loglan, and some of its features come from Láadan. The characteristic regularity, unambiguity, and versatility of Lojban grammar owes much to modern linguistics and computer programming—resources that were unavailable to the designers of earlier languages. Lojbanist Bob LeChevalier summarized one advantage of Lojban grammar as follows: "Lojban moves beyond the restrictions of European grammar. It overtly incorporates linguistic universals, building in what is needed to support the expressivity of the whole variety of natural languages, including non-European ones."^[1]

Lojban texts can be parsed just as texts in programming languages are by using formal grammars such as PEG, YACC, Backus–Naur form.^[2] There are several parsers available.^[3][4][5]

Lojban has 6 vowels and 21 consonants. The phonemes are commensurate with graphemes, which means Lojban has 27 letters (lerfu) each corresponding to a unique phoneme. Lojbanic graphemes can vary in mode; this article employs the Latin alphabet version, which is currently in the most common usage (see Orthography for more detail). The phonemes, on the other hand, are defined solely according to the International Phonetic Alphabet.

The tables below show typical realizations of sounds and the Latin alphabets in Lojban. In all cases except the rhotic consonant the first phoneme represents the preferred pronunciation, while the rest are the permitted variants intended to cover dissimilitude in pronunciation by speakers of different linguistic backgrounds.

Note that simple vowel graphemes are never diphthongized like in English. Diphthongs are always written with two vowel graphemes.

	Phoneme	Latinate grapheme	English pronunciation example
vowels
open vowel	a (ɑ)	a	as in father
front mid vowel	ɛ (e)	e	as in bet
front close vowel	i	i	as in machine
back mid vowel	o (ɔ)	o	as in open
back close vowel	u	u	as in moon
central mid vowel	ə	y	as in sofa
fricatives
unvoiced labial fricative	f (ɸ)	f	as in fan
voiced labial fricative	v (β)	v	as in van
unvoiced velar fricative	x	x	as in the Scottish loch, the German Bach, the Spanish José, or the Arabic Khaled
unvoiced glottal spirant	h	'	as in hat
sibilants
unvoiced alveolar sibilant	s	s	as in sing
voiced alveolar sibilant	z	z	as in zero
unvoiced coronal sibilant	ʃ (ʂ)	c	as in shoe
voiced coronal sibilant	ʒ (ʐ)	j	as in vision
stops
unvoiced bilabial stop	p	p	as in pip
voiced bilabial stop	b	b	as in bib
unvoiced alveolar stop	t	t	as in tap
voiced alveolar stop	d	d	as in dance
unvoiced velar stop	k	k	as in kink
voiced velar stop	ɡ	g	as in girl, not as in gym
glottal stop	ʔ	.	as in uh-oh
approximants
voiced labio-velar approximant	w	u-	as in winter
palatal approximant	j	i-	as in you
voiced lateral approximant	l (l̩)	l	as in luck
nasals
voiced labial nasal	m (m̩)	m	as in minimum
voiced alveolar nasal	n (n̩, ŋ, ŋ̩̩)	n	as in noon
rhotic
rhotic consonant	r (ɹ, ɾ, ʀ, r̩, ɹ̩, ɾ̩, ʀ̩)	r	as in red; or as in Spanish pero or perro, or French rendez-vous

Lojban has 16 diphthongs, vowels that change quality during their emission but always being single syllable nuclei like pure vowels. Unlike English and similarly to languages such as Spanish, diphthongs are not distinct phonemes by themselves but are analyzed as a combination of "semi-vowel + vowel" (or the inverse order). The combinations <ai>, <au>, <ei> and <oi>, for instance, are all realized as the corresponding falling diphthongs. Triphthongs exist as combinations of a rising and a falling diphthong, e.g. <iau>.^{[citation needed]}

The vowels can be either rounded or unrounded. The consonants can be either aspirated or unaspirated, although the voiceless stops /p/, /t/ and /k/ are usually aspirated to some degree. In general, consonants are not palatalized. The affricates /d͡ʒ/, /t͡ʃ/, /d͡z/, and /t͡s/ occur in Lojban (like in English jar, chair, fads, and cats.), but they are not distinct phonemes, contrary to English /d͡ʒ/ and /t͡ʃ/. Each is considered to be a combination of an appropriate stop and fricative phoneme: the sequences <dj>, <tc>, <dz> and <ts>, respectively. The rhotic sounds are all equally acceptable as an identical phoneme.^[6] ⟨l⟩, ⟨m⟩, ⟨n⟩, and ⟨r⟩ may be syllabic.^[7]

For those who, given their native language background, may have trouble pronouncing (certain) consonant clusters, there is the option of inserting buffer vowels between them, as long as they differ sufficiently from the phonological vowels and are pronounced as short as possible. This mechanism can be described as a form of anaptyxis (vocalic epenthesis). Possible choices include [ɪ] , [ɨ], [ʊ] and [ʏ] (but not [y], which is the rounded counterpart of [i] and thus a valid realization of /i/). The resulting added syllables are completely ignored by the grammar, including for the purposes of stress determination.

Lojban may be written in different orthography systems as long as it meets the required regularities and unambiguities. Some of the reasons for such elasticity would be as follows:

1. Lojban is rather defined by the phonemes (spoken form of words), therefore, as long as they are correctly rendered so as to maintain the Lojbanic audio-visual isomorphism, a representational system can be said to be an appropriate orthography of the language;
2. Lojban is meant to be as culturally neutral as possible, so it is never crucial or fundamental to claim that some particular orthography of some particular languages (e.g. the Latin alphabet) should be the dominant mode.

Lojbanist Kena extends this principle to argue that even an original orthography of the language is to be sought.^[8]

Lojban's Latin alphabet consists of 23 lerfu a b c d e f g i j k l m n o p r s t u v x y z plus 3 semi-lerfu ' , . which are used. They are intentionally ordered in accordance with that of ASCII characters.

Capitalization may be applied to mark a non-standard stressed syllable as in cmevla, but they are not considered separate lerfu. Whether a single vowel or the entire syllable is capitalized is a matter of preference; for example, the name "Josephine" can be rendered as either DJOzefin. or djOzefin. (without the capitalization, the ordinary rules of Lojban stress will cause the 'ze' syllable to be stressed instead).

Punctuation marks are not mandatory; such notions as question or exclamation are expressed with words rather than unpronounced symbols.^[9]

This mode was conceived when the introductory Lojban brochure was translated into Russian. 23 lerfu а б в г д е ж з и к л м н о п р с т у ф х ш ъ plus 3 semi-lerfu ', . are used. The hard sign ъ is assigned to the open-mid vowel (as in Bulgarian). Diphthongs are written as vowel pairs, as in the Roman mode.^[10]

Kena^[11] argues for writing Lojban using Tengwar, arguing that:

1. the Latin alphabet is too strongly related to Western civilizations, and thus probably introduces some kind of cultural bias in Lojban. Lojban wants to be both logical and culturally neutral, the Tengwar already are;
2. the Tengwar system inherently contains some main Lojban morphology rules, making Lojban easier to learn when it is written with Tengwar.

Advocates of this mode include Eric S. Raymond.^[12]

Another option for cultural neutrality (free from fictional cultures even) is the zbalermorna alphabet.^[13]

A Japanese hiragana version of Lojban orthography has been proposed, in which case more than 80 lerfu may be used. This mode is not without certain technical issues since the hiragana (and katakana too) are always syllabic, indicating an open syllable (with the exception of the final "n" sound), requiring some special attention when representing the Lojbanic consonant clusters.^[14] Several example haiku compositions in the orthography have been created.^[15][16]

This section needs expansion. You can help by adding to it. (August 2007)

Lojban has 3 word-classes: brivla (verbs or predicate words), cmavo (structure words), and cmevla (name words). Each of them has uniquely identifying morphological properties, so that one can unambiguously recognize which word is of which part of speech in a string of the language. They may be further divided in sub-classes (discussed respectively below).^[17]

There also exist affixes (rafsi) assigned to some of the brivla and cmavo.^[18][19]

brivla carry the content (semantic information) of an expression. The bare brivla corresponds to the verb in English. Additional words can be used to transform it into what corresponds to English common nouns, adjectives, or adverbs^[20] (although some modal cmavo too may have adverbial purposes^[21]). Brivla may be identified by the following morphological properties:^[22]

• Have more than one syllable
• Are penultimately stressed
• Have a consonant cluster (at least two adjacent consonants) in the first 5 lerfu including the second consonant
• Start with a consonant (except some fu'ivla)
• End with a vowel

A word such as lobypei will still be considered as a brivla because the special gluing vowel y between b and p is to be ignored and therefore a consonant cluster (b-p) assumes its existence within it.

Unlike verbs in English, brivla do not inflect for tense, person, or number.

Brivla's sub-classes are as follows, with some examples.

The brivla which constitute the lexical core of the language are called gismu. They are invariably five-letter words, which distinguishes it from the other types of brivla, and are in a form of either CVCCV or CCVCV (C stands for a consonant and V for a vowel). Being two syllables means that the general rule of brivla to be stressed penultimately will always cause the first syllable of a gismu to be stressed.

They have been chosen or added as root words because they

• represent concepts that are very familiar and basic,
• represent concepts the usage of which is equally frequent among different languages,
• would be helpful in constructing more complex words, or
• represent fundamental grammatical concepts of Lojban.^[18]

The main source languages from which they were drawn are Arabic, Chinese, English, Hindi, Russian, and Spanish. Here is further explanation of the nature of gismu by Cowan:

The gismu do not represent any sort of systematic partitioning of semantic space. Some gismu may be superfluous, or appear for historical reasons: the gismu list was being collected for almost 35 years and was only weeded out once. Instead, the intention is that the gismu blanket semantic space: they make it possible to talk about the entire range of human concerns. [...] For a given concept, words in the six languages that represent that concept were written in Lojban phonetics. Then a gismu was selected to maximize the recognizability of the Lojban word for speakers of the six languages by weighting the inclusion of the sounds drawn from each language by the number of speakers of that language.

The Complete Lojban Language: 4.4

According to Robin Turner,^[23] the creation was algorithmically done by computer.

Approximately 1350 gismu exist, which is a relatively small number when compared to that of English words ranging from 450,000 up to 1,000,000.^[24] Theoretically, by learning only these root words, as well as their fragmental forms and some major structure words (cmavo), one will be able to communicate effectively in Lojban.

The form of brivla made of affixes (rafsi) is called lujvo.

fu'ivla usually refers to things that are culture-specific (including Lojban culture) or to kinds of plants or animals, concepts which cannot be easily expressed as mere modifying-modified combinations of Lojban's internal root verbs (gismu).

fu'ivla can be subdivided into four types according to the extent to which they are modified, namely Stage 1, 2, 3, and 4 fu'ivla.

The longest form, quoting a foreign word/phrase while preserving its original spelling with particular structure words.

• A "hybrid" stage sometimes is enlisted. In this case, it would take the above sentence but Lojbanize "spaghetti" to be phonetic to a (native) Lojban without changing the ending. Therefore, stage "1.5" fu'ivla for "spaghetti" is "me la'o ly. spageti ly."

This stage involves lojbanizing the sound and spelling of the word.

me la .spagetis.
(me is still needed since la spagetis. cannot by itself work as a brivla.)

At this stage a borrowed word is fully turned into a single brivla, having its own place structure. Since no brivla may have more than one meaning, it is often the case that they are attached by a rafsi (with a hyphen like "-r-", "-n-", or "-l-") categorizing or limiting the semantic scope of the word (such are called "rafsi classifier"). Again they always start with a consonant and end with a vowel.

These are the borrowings which are so common or so important that have become as short as possible, having no rafsi classifier. Unlike other brivla, they may begin with a vowel (preceded by a pause mark separating it from the previous word). Also the word must not be of a form that one can remove all the initial vowels (and apostrophes) and have a valid word.

It is possible to absorb a fu'ivla into a lujvo, with principles varying among Lojbanists. Notable proponents are Pierre Abbat and Jorge Llambías. Here are some comparisons of their methods drawn from the Lojban mailing list (as of July 2007):

Lojban particles, cmavo, are recognized by following morphological properties:

• may be a single syllable
• never contain a consonant cluster of any type, whether or not y is counted
• end in a vowel
• need not be penultimately stressed, though they often are if they have more than one syllable

And they display one of the following letter patterns: V, VV, V'V, CV, CVV, CV'V. The form generally does not indicate anything about its grammatical function.

cmavo can be sequenced without spaces and without any change to its meaning:

As far as the stress rules of Lojban are concerned, such compound cmavo are still separate words, so penultimate stress (e.g. paREci) is not obligatory.

Some cmavo have rafsi, which may help converting tanru (sequence of brivla) into lujvo:

This section is empty. You can help by adding to it. (February 2022)

cmevla are mostly used for names of things (including people) in descriptions or in direct address (cf. proper nouns). They can be in any form as long as they end in a consonant. The practice by which names in natural languages are modified to be used in Lojban is known as "lojbanization".

la .bionses.nolz., (a possible realization of the name "Beyoncé Knowles")

A special building block, from which a new lujvo may be created, is called rafsi. Rafsi are bound to certain gismu, cmavo or fu'ivla. This also means that lujvo have no rafsi form of their own. Rafsi cannot by themselves function as an individual words; they only form lujvo when at least two are joined together.

The unambiguity of Lojban morphology, according to John Woldemar Cowan, gives rise to "significant clues to the meaning and the origin of the word, even if you have never heard the word before". He further says: "The same principle allows you, when speaking or writing, to invent new brivla for new concepts 'on the fly'; yet it offers people that you are trying to communicate with a good chance to figure out your meaning. In this way, Lojban has a flexible vocabulary which can be expanded indefinitely."

According to What Is Lojban?,^[25] the language's grammatical structures are "defined by a set of rules that have been tested to be unambiguous using computers", which is called the "machine grammar". Hence the characteristics of the standard syntactic (not semantic) constructs in Lojban:

• each word has exactly one grammatical interpretation;
• the words relate grammatically to each other in exactly one way.

Such standards, however, are to be attained with certain carefulness:

It is important to note that new Lojbanists will not be able to speak 'perfectly' when first learning Lojban. In fact, you may never speak perfectly in 'natural' Lojban conversation, even though you achieve fluency in the language. No English speaker always speaks textbook English in natural conversation; Lojban speakers will also make grammatical errors when talking quickly. Lojbanists will, however, be able to speak or write unambiguously if they are careful, which is difficult if not impossible with a natural language.

Nick Nicholas and John Cowan. What Is Lojban? II.3

The computer-tested, unambiguous rules also include grammar for 'incomplete' sentences e.g. for narrative, quotational, or mathematical phrases.

Lojbanic expressions are modular; smaller constructs of words are assembled into larger phrases so that all incorporating pieces manifest as a possible grammatical unity. This mechanism allows for simplistic yet infinitely powerful phrasings; "a more complex phrase can be placed inside a simple structure, which in turn can be used in another instance of the complex phrase structure".

Being derived from predicate logic, the basic unit of Lojban expression is predication, a claim that some objects stand in some relationship, or that some single object has some property. In Lojban they are expressed using clauses (bridi). Just as a predication is formed by a predicate and arguments in formal logic, bridi are formed by selbri and sumti in Lojban. In linguistic terms selbri is the predicate of a clause, and sumti are its arguments. A construct of selbri and sumti produces a claim that something stands in a specified relationship to something else or has a specified property.

Multiple bridi can be either sequenced across multiple sentences or compounded in one sentence:

A compound bridi can include multiple tenses and sumti:

The implicit grammatical divisions can be made explicit by separator words such as cu and vau, which are often elidable but sometimes need to be present to avoid ambiguity:

The places of cu and vau in the previous examples can be rendered as follows:

The ordered sets of sumti assigned to every selbri are known as "place structures". They are explicitly defined in dictionaries or word lists.

mi | tavla | do | la .lojban. | le glibau
(Two sumti mi and do are fitting into the place structure of the selbri tavla, which is "x1 talks/speaks to x2 about subject x3 in language x4".)

Some lujvo formations usually operate on the place structure in predictable ways. The rafsi gau, for instance, inserts one place for the agent and pushes all others down one. Thus brivla can have indefinitely many places. This contrasts with the accusative alignment or ergative alignment that most languages have, in which there is a small number of named places (subject, direct object, indirect object) and all others are expressed by prepositions.

The word order in Lojban is basically free. All the following sentences mean "I love you", differing only in word order:

Such flexibility has to do with the language's intended capability to translate as many expressions of natural languages as possible, based on a unique positional case system. The meaning of the sentence mi prami do is determined by prami realizing, with its own predefined place structure, a specific semantic relation between mi and do; when the positional relation between mi and do changes, the meaning of the sentence changes too. As shown above, Lojban has particular devices to preserve such semantic structure of words while altering their order. Compare the followings:

se converts the x1 and x2 sumti place. fo tags the x4 place, and fi the x3. Such conversion and tagging is often used to emphasize particular sumti by bringing it forward.

Here are some collations of natural languages and Lojban:

It is important to note that Lojban selbri is not a real equivalent of verb in natural languages. A selbri can be either a verb, a noun, an adjective, or an adverb. Its function is determined syntactically, not morphologically. An analogy to natural language word orders by using such terms as "subject", "verb", and "object" cannot accurately describe the nature of Lojban bridi.

There are five kinds of simple sumti:

1. descriptions, which usually begin with a descriptor such as le or more commonly now lo;
2. pro-sumti, the Lojban analogue of pronouns, such as mi;
3. names, which usually begin with la, such as la .lojban.;
4. quotations, which begin with lu, lo'u, zo, zoi;
5. pure numbers, which usually begin with li.

Basic descriptions in Lojban consist of two units, LE/LA descriptors and a selbri:

le zarci

Although le is quite close in meaning to English "the", it has particularly unique implications. In this example, le creates an argument which might occur in the x1 place of the belonging selbri zarci, namely a "market". le also specifies that the speaker 1) has one or more specific markets in mind (whether or not the listener knows which ones they are) and 2) is merely describing the things he/she has in mind as markets, without being committed to the truth of that description. Whereas English-speakers must differentiate between "the market" and "the markets", Lojban-speakers are not required to make such a choice (this rule does not mean that Lojban has no way of specifying the number of markets in such a case):

le zarci cu barda
The market is big. / The markets are big.

Since the construct le + selbri merely describes something or other which the speaker chooses to represent based on his/her observation, such an expression as follows is possible:

le nanmu cu ninmu
one-or-more-specific-things-which-I-describe as "men" are women

While le is specific, lo is not:

lo zarci cu barda
one-or-more-of-all-the-things-which-really are-markets is/are-big
A market is big. / Some markets are big.

lo refers generally to one or more markets, without being specific about which. Unlike le zarci, lo zarci must refer to something which actually is a market (that is, which can appear in the x1 place of a truthful bridi whose selbri is zarci). lo morsi cu jmive is false as there are no objects in the real world which are both dead and alive.

la dissociates the subsequent selbri from its normal meaning, usually making a name (this usage should not be confused with the other usage before regular Lojbanized names). Like le descriptions, la descriptions are implicitly restricted to those the speaker has in mind:

la cribe pu finti le lisri
the-one-named "bear" [past] creates the story.
Bear wrote the story.

All descriptions implicitly terminate with ku, which can almost always be omitted with no danger of ambiguity. The main exceptions are a) when relative clauses are involved and b) when a description immediately precedes the selbri (in which case using an explicit cu before the selbri makes the ku unnecessary). Other usages of ku include making a compound negator (naku) and terminating place-structure/tense/modal tags (puku, baiku).

The selbri is the logical predicate of a bridi. This is not to be confused with the meaning of predicate in terms of the English Language, but as a logical predicate. Whereas a predicate in English contains everything that the subject is doing, a logical predicate is simply the relation between all involved parties. In this context, the selbri is roughly the equivalent of a verb in English. For instance:

The gismu nelci is being used as the selbri in this bridi. It is describing the relationship between the sumtis mi (I) and le gerku (the dog). The relationship is that of a liker and that which is liked. The roles in the relationship are determined by the sumti placements inherent in the word being used as the selbri. The cmavo se/te/ve/xe are used to swap the first sumti placement of the selbri with the second, third, fourth, and fifth sumti placement, respectively. This functionality allows for the flexibility in bridi. For instance, the gismu klama has the sumti of:

• x1: One which goes
• x2: The destination of a goer
• x3: The source of a goer
• x4: The route taken by a goer
• x5: The vehicle used by a goer

Thus:

Selbri can also be tanru, where the sumti placements are determined by the last brivla that is part of the tanru. For instance:

This section needs expansion. You can help by adding to it. (August 2007)

A group of two or more selbri put one after another is called tanru and acts as a single selbri (while the selbri it is composed of are called tanru units (selbrisle)). They correspond to English compound verbs like drip fry or drip dry.

Tanru can be converted to sumti as usual selbri.

Tanru may be used so as to more specifically conceptualize the intended meaning. In lo skami pilno ("computer user(s)"), there is a tanru skami pilno where the modifying brivla skami narrows the sense of the modified brivla pilno to form a more specific concept (in which case the modifier may resemble English adverbs or adjectives). Without skami, lo pilno will just mean "user". Other examples:

Arguments of selbri representing tanru units may be filled as well, in which case they are attached using the particle be (starting from x2 place of the tanru unit):

The cmavo consist of various particles and structure words.^[26] These include descriptors, connectives, attitudinals, prepositions, and tense words.

There are five descriptors (gadri in Lojban): lo, le, la, li, and me'o; of which the first three inflect to show individual, mass, or set (though as far as the formal grammar is concerned, the inflected forms are separate words, not inflected forms).

	Individual	Mass	Set	Typical
Indefinite	lo	loi	lo'i	lo'e
Definite	le	lei	le'i	le'e
Name	la	lai	la'i	–
Number	li	–	–	–
Mathematical expression	me'o	–	–	–

The individual/mass distinction is similar to the distinction between mass nouns and count nouns, but things that are normally counted can be considered as a mass. The set articles consider the mathematical set of the referents.

The number and mathematical expression articles are used when talking about numbers and numerals or letters as themselves.

Note that gadri are sometimes called articles, which doesn't correspond to the usual notion of articles in linguistics.

As befits a logical language, there is a large assortment of conjunctions.

There exist 16 possible different binary truth functions, the four fundamental ones of which are assigned four vowels in Lojban. These vowels are a component sound from which actual logical-connective cmavo are built up.

A	FIRST is true and/or SECOND is true (TTTF)
E	FIRST is true and SECOND is true (TFFF)
O	FIRST is true if and only if SECOND is true (TFFT)
U	FIRST is true whether or not SECOND is true (TTFF)

With the four vowels, the ability to negate either sentence (with na or nai), and the ability to exchange the sentences, as if their order had been reversed (with se), Lojban can create all of the 16 possible truth functions except TTTT and FFFF.

	Original form	Negating first	Negating second	Negating both
A	(A) .a (B)	(A) na.a (B)	(A) .anai (B)	(A) na.anai (B)
	${\displaystyle A\lor B}$	${\displaystyle \neg A\lor B}$ ${\displaystyle A\rightarrow B}$	${\displaystyle A\lor \neg B}$ ${\displaystyle A\leftarrow B}$	${\displaystyle \neg A\lor \neg B}$ ${\displaystyle A\uparrow B}$
	A or B	If A, then B	A if B	A NAND B A or B, not both
E	(A) .e (B)	(A) na.e (B)	(A) .enai (B)	(A) na.enai (B)
	${\displaystyle A\wedge B}$	${\displaystyle \neg A\wedge B}$ ${\displaystyle A\nleftarrow B}$	${\displaystyle A\wedge \neg B}$ ${\displaystyle A\nrightarrow B}$	${\displaystyle \neg A\wedge \neg B}$ ${\displaystyle A\downarrow B}$
	A and B	Not A but B	A but not B	Neither A nor B
O	(A) .o (B)	(A) na.o (B)	(A) .onai (B)	(A) na.onai (B)
	${\displaystyle A\leftrightarrow B}$	${\displaystyle \neg A\leftrightarrow B}$ ${\displaystyle A\oplus B}$	${\displaystyle A\leftrightarrow \neg B}$ ${\displaystyle A\oplus B}$	${\displaystyle \neg A\leftrightarrow \neg B}$ ${\displaystyle A\leftrightarrow B}$
	A if and only if B	A or B, not both	A or B, not both	A if and only if B
U	(A) .u (B)	(A) na.u (B)
	${\displaystyle A}$	${\displaystyle \neg A}$
	A, regardless of B	Not A, regardless of B
	(A) se.u (B)	(A) se.unai (B)
	${\displaystyle B}$	${\displaystyle \neg B}$
	Regardless of A, B	Regardless of A, not B

.onai is preferred over na.o. Note that in se.unai, the negation occurs before "swapping" the positions of A and B. While se can be used for the other connectives, it is unnecessary since or, and, and if and only if have the same relationship if their inputs are swapped (i.e. they are commutative).

FFFT	(A) na.enai (B)	${\displaystyle A\downarrow B}$	Neither A nor B
FFTF	(A) na.e (B)	${\displaystyle A\nleftarrow B}$	Not A but B
FFTT	(A) na.u (B)	${\displaystyle \neg A}$	Not A (regardless of B)
FTFF	(A) .enai (B)	${\displaystyle A\nrightarrow B}$	A but not B
FTFT	(A) se.unai (B)	${\displaystyle \neg B}$	(Regardless of A) Not B
FTTF	(A) .onai (B)	${\displaystyle A\oplus B}$	A or B, not both
FTTT	(A) na.anai (B)	${\displaystyle A\uparrow B}$	A NAND B
TFFF	(A) .e (B)	${\displaystyle A\wedge B}$	A and B
TFFT	(A) .o (B)	${\displaystyle A\leftrightarrow B}$	A if and only if B
TFTF	(A) se.u (B)	${\displaystyle B}$	(Regardless of A) B
TFTT	(A) na.a (B)	${\displaystyle A\rightarrow B}$	If A then B
TTFF	(A) .u (B)	${\displaystyle A}$	A (regardless of B)
TTFT	(A) .anai (B)	${\displaystyle A\leftarrow B}$	A if B
TTTF	(A) .a (B)	${\displaystyle A\lor B}$	A or B

In order to remain unambiguous, each place in the grammar of the language where logical connection is permitted has its appropriate set of connectives. If the connective suitable for sumti were used to connect selbri, ambiguity would result. Connections between components other than sumti can be expressed as follows (note that their functions are in accordance with the assigned vowels):

Negatives and se can be used with these connectives with similar forms.

Connections can also be given using "forethought" forms

Negatives are created by adding nai to the connective before the negated construct.

Connections can be questioned:

Besides the logical connectives, there are several non-logical connectives. These do not change form depending on what they are connecting:

(A) joi (B)	the mass with components A and B
(A) ce (B)	the set with elements A and B
(A) ce'o (B)	the sequence with elements A and B in order
(A) sece'o (B)	the sequence with elements B and A in order
(A) jo'u (B)	A and B considered jointly
(A) fa'u (B)	A and B respectively
(A) sefa'u (B)	B and A respectively
(A) jo'e (B)	the union of sets A and B
(A) ku'a (B)	the intersection of sets A and B
(A) pi'u (B)	the cross product of sets A and B
(A) sepi'u (B)	the cross product of sets B and A

The ku is required by the LALR parser, but not by the PEG parser, which however is not official yet.

Attitudinals are a set of cmavo which allow the speakers to express their emotional state or source of knowledge, or the present stage of discourse. In natural languages, attitudes are expressed using interjections, but also by the tone of voice when speaking, and (very imperfectly) by punctuation when writing; in Lojban, such information are extensively expressible in words. And the meanings are to be understood separately from the main predicate.

They may be "scaled" by suffixes:

Combination is possible, and highly productive as well as creative:

Evidentials, derived from those of American Indian languages and the constructed language Láadan, show how the speaker came to say the utterance, i.e. the source of the information or the idea:

There are two kinds of prepositions (sumtcita, which refers to adpositions in general) in Lojban: tense markers and proper prepositions. The syntactic difference is that a proper preposition can be converted with se, whereas a tense marker cannot. All proper prepositions (except the vague one do'e) are formed from a brivla and mark their object semantically as being in a place of that brivla. Thus the following are equivalent:

Prepositions (including tense markers) can also be placed in .i ... bo to make sentence conjunctions. With most prepositions this makes no sense, but ki'u, ja'e, mu'i and ni'i are often used this way to express various kinds of "because" and "therefore":

la .djan. cpacu le pamoi se jinga .iki'ubo ri jinga
John got the first prize because he won.

Lojban has 63 unique tense words to express various aspects of both space and time as well as event: such a system is unusual among other languages, in that it deals with spatial and temporal aspects in the same term. Simply put, these tense words are used to show where and when the event is taking place, relative in space-time to when the sentence is spoken. They can be roughly subdivided as follows:

Intervals	pu (before), ca (during), ba (after), bu'u (at/coincident with), ne'a (next to), re'o (adjacent to), te'e (bordering), pa'o (passing through), ne'i (within), fa'a (towards), to'o (away from), ze'o (outward), zo'a (inward), zo'a (passing by/tangential to), ga'u (above), ni'a (below), ca'u (in front of), ti'a (behind), ri'u (to the right of), zu'a (to the left of), be'a (north of), ne'u (south of), vu'a (west of), du'a (east of), ru'u (surrounding), cu'e (when/where, as a question word)
Modifiers	zi (a short time away), za (a medium-length time away), zu (a long time away), vi (a short distance away, here), va (a medium distance away, near), vu (a long distance away, there), ze'i (for a short time), ze'a (for a medium-length time), ze'u (for a long time), ze'e (for the whole time), ve'i (in a small area), ve'a (in a medium-sized area), ve'u (in a large area), ve'e (in the whole area), vi'i (along a (1D) line), vi'a (throughout a (2D) area), vi'u (throughout a (3D) space), vi'e (throughout a (4D) spacetime)
Contours	ca'o (continuative, during), pu'o (anticipative, until), ba'o (perfective, since), co'a (initiative, at the start), co'i (achievative, at instantaneous point of), co'u (cessative, at the end even if premature), mo'u (completive, at natural end), za'o (superfective, continuing after natural end), de'a (pausative, temporary pause), di'a (resumptive, continuing after pause)
Converters	mo'i, fe'e, roi, re'u, jai, ki

The "converters" require further explanation: mo'i marks that the movement is towards (or away from, etc.) a point rather than at a point, so that be'a, meaning "(occurring) in the north", becomes mo'ibe'a, "(heading) northward"; roi marks the number of times an event takes place, e.g. paroi (once), roroi (always), noroi (never), re'u indicated an ordinal, e.g. pare'u, first time; fe'e marks an interval in space rather than in time, so that, for example, fe'e co'a is the "beginning point" of something physically extending in a given direction; jai is used to mark tense words that have been moved in a sentence, comparable to se/te/ve/xe and fa/fe/fi/fo/fu for sumti; ki marks a "sticky tense", as explained below.

Marking tenses is always optional in Lojban:

Where the tense information is not specified, the context resolves the interpretation.

Tense words are usually put right before the selbri:

mi [cu] pu klama le zarci (cu is the implicit separator between the first sumti mi and the selbri klama.)

They may be placed elsewhere with the additional terminator ku:

The terminator is used so that the tense word do not directly run into the following sumti and modify it. Compare the next sentences:

Tenses can be "layered up":

mi pu klama le zdani .i le zdani pu pu se daspo
I [past] go-to the house. The house [past][past] be-destroyed.
I went to the house. The house had been destroyed.

Tenses can be "sticky" by being set with ki, continuing in effect over more than a single bridi, until it is unset:

mi pu ki fengu binxo .i le nixli cu klaku cfari .i mi ki xenru
I [past]-[set this tense] angry-kind-of become. The girl crying-kind-of start. I [set this tense] regret.
(Earlier) I got angry. The girl started crying. (Now) I regret.

The second ki resets the tense to the implicit default time from the speaker's point of view, which is "now" (this means that ki may be used as a tense word by itself).

Using ki, equivalents of the previous layering tenses can be produced:

mi puki klama le zdani .i le zdani pu se daspo

The second pu is to be counted from the tense set by the last ki, so in effect it is equivalent to pupu.

Similar to the tense words are a collection of words to show potentiality: ca'a, "actually is"; ka'e, "is innately capable of"; nu'o, "can but has not"; pu'i, "can and has". These words operate in the same way as tense words.

Semantic unifications and combinations are performed by word groupings, each include a starting and a | often elidable) terminating cmavo. Here basic example sentences with them are ordered by their terminating cmavo:

Lojban	English	Notes
ti xamgu be le tifri bei lo togmo'a po ko'a be'o selsa'a cu se nelci	This for the audience in view of its melody good song is liked.[27]
ti selsa'a fi'o xamgu zukte fe'u lo barda jgita cu se nelci	This with a big guitar well played song is liked.[28]
ti selsa'a ji'a ne ta gugde ge'u ki'u le finti pu clira zmadu xabju va	This song is also incidentally associated with that country because the author once lived there.
po'o le selsa'a pe ta gugde ge'u .e na drata cu se nelci va	Only the songs associated with that country are liked there, others not.
ti selsa'a po ta gugde ge'u se pilno fi gricniselsa'a va	This song which is owned by that country is used as anthem there.	instead of po: no'u would mean the song is incidentally also the same as the country, po'e the country inalienably possessed the song and po'u would mean only such a song which is the same as the country.
ti selsa'a ge se finti gi se pilno fi gricniselsa'a vau nenri ti gugde	This song is in this country both created and used as anthem.	Instead of both ... and represented by ge also other logical connections from selma'o GA, GUhA or JOI are possible.
ti selsa'a cu sarcu tolcau ka xamgu togmo'a kei .ijanai do djica lo nu ko'a misno binxo	One property of this song will have to be a good melody if you want it to become famous.
li'i zukte ti selsa'a kei po mi cu banzu lo terva'i ko'a ka xamgu	My experience about playing this song is sufficient for estimating how good it is.
le nu so'i xamgu zukte kei misno selsa'a cu se nelci.	The due to many good playings famous song is liked.	Instead of nu: jei would mean the many good playings are a truth value, mu'e they are an in time more focused event, ni they are a quantity/amount, pu'u a process, si'o an idea/concept, za'i a continuous state, zu'o an activity and su'u a not furtherly classified grouping like also the following groupings while only they does not mean abstractions: a ke ... ke'e grouping, a fu'e ... fu'o grouping before which enclosed attitudinal, evidential and discursive cmavo have no meaning, a me ... me'u grouping which means specifically a sumti to selbri conversion and a tu'e ... tu'u grouping which groups multiple sentences or paragraphs.
le/lo selsa'a ra'i ta gugde ku se nelci va	The/A song from that country is liked there.	Also for groupings of the Descriptors lei, loi, le'i and lo'i is ku the terminator.
ti selsa'a poi fange finti pu stidi za'i ke'a gricniselsa'a ti gugde ku'o se pilno vi ta tadji	This song which a foreign author proposed as anthem for this country is used here that way.	noi instead of poi would mean only additional instead of restrictive description about the song.[29] If the relative clause's context is more discursive and metalinguistic a sei ... se'u grouping and if its association is even less then parenthesis grouping to ... toi can be used instead.
ti sagypemci vasru lo'u ti gugde cu banli .i ko banro .e za'i snada le'u	It is questionable whether this song lyrics should comprise "This country is great. Grow and prosper!"
ti sagypemci vasru lu ti gugde cu banli .i ko banro .e za'i snada li'u	This song lyrics comprise "This country is great. Grow and prosper!"	For 1-word quotations also only cmavo zo can be used before it.
la'e le selsa'a lu'u cu certu preni ku'i lo selsa'a se'i cu xlali	The ones who refer to the song are smart people but the song itself is bad.
soi mi pilno ji'a so'o selsa'a po ko'a se'u nenri lo zdani po mi'a	I use also some songs of him/her and vice versa, in our house.[30]	Furthermore ku'e,[31] lo'o,[32] te'u[33] and ve'o[34] are terminators for mathematical expressions.

• Cowan, John Woldemar (2016) [1st ed. 1997]. The Complete Lojban Language (2nd ed.). The Logical Language Group, Inc. ISBN 978-0966028324. Retrieved 2016-07-26.

• The Lojban Reference Grammar with Errata
• Example Tengwar mode
• Another example Tengwar mode