This article is an informal outline of the grammar of Interlingua, an international auxiliary language first publicized by IALA. It follows the usage of the original grammar text (Gode & Blair, 1951), which is accepted today but regarded as conservative.
The grammar of Interlingua is based largely on that of the Romance languages, but simplified, primarily under the influence of English. However, all of the control languages, including German and Russian, were consulted in developing the grammar. Grammatical features absent from any of the primary control languages (English, French, Italian, Spanish and Portuguese) were dropped. For example, there is neither adjectival agreement (Spanish/Portuguesegatos negros 'black cats'), since this feature is absent in English, nor continuous verb tenses (English I am reading), since they are absent in French. Conversely, Interlingua has articles, unlike Russian, as Russian is a secondary control language.
There is no systemic marking for parts of speech. For example, nouns do not have to end in any particular letter. Typically, however, adjectives end in -e or a consonant, adverbs end in -mente or -o, while nouns end in -a, -e, -o or a consonant. Finite verbs virtually always end in -a, -e, or -i, while infinitives add -r: scribe, 'write', 'writes'; scriber, 'to write'.
The definite article is le, the indefinite article is un, and neither article shows any agreement in form with nouns. The prepositions a ("to") and de ("of") fuse with a following le into al and del respectively.
The definite article is, on the whole, used as in English, with the exception that it should not be omitted with titles preceding proper names nor with abstract nouns representing an entire class, species, etc.
Nouns
Nouns inflect for number only. Plural nouns take -s after a vowel, -es after a consonant (but final -c and "g" changes in spelling to -ches (and Ghes) to preserve the [kandg] sound of c and g).
catto 'cat' → cattos 'cats'
can 'dog' → canes 'dogs'
roc 'rook' [chess] → roches 'rooks'
Interlingua has no grammatical gender. Animate nouns are sex-neutral, unless they refer specifically to a male or a female. Thus, jornalista 'journalist' and scientista 'scientist' are sex-neutral, while rege 'king' and regina 'queen' are sex-specific. Explicit feminine forms can be created by substituting final -a for a final -o or -e or by adding the suffix -essa.
puero 'boy' → puera 'girl'
tigre 'tiger' → tigressa 'female tiger'
These colour the regular forms as masculine when they appear in the same context.
Unlike in English, nouns cannot take adjectival forms, such as 'winter weather', 'research laboratory', 'fall coat', etc. Such constructions instead require the use of a preposition or a corresponding adjective, respectively tempore hibernal, laboratoria de recerca, and mantello pro autumno. This is however excepted by proper nouns which can be used adjectivally as in English: contator Geiger 'Geiger counter', motor Diesel 'Diesel engine', radios Röntgen 'Roentgen rays', etc.
Despite the above restrictions, Interlingua permits use of apposition, which is often equivalent to adjectival nouns in English.
arbore nano 'dwarf tree'
nave domo 'house boat'
Male and female forms should match.
Adjectives
Adjectives may precede or follow the noun they modify. As a matter of style, short adjectives tend to precede, long adjectives tend to follow. Numerals always precede the noun.
belle oculos or oculos belle 'beautiful eyes'
un bon idea, un idea ingeniose 'a good idea, an ingenious idea'
An adjective never has to agree with the noun it modifies, but adjectives may be pluralized when there is no explicit noun to modify.
le parve infantes 'the little children'; but le parves 'the little ones'
Comparative degree is expressed by plus or minus preceding the adjective and superlative degree by le plus or le minus.
un plus feroce leon 'a fiercer lion'
un traino minus rapide 'a less speedy train'
le plus alte arbore 'the tallest tree'
le solution le minus costose 'the least costly solution'.
The suffix -issime may be used to express the absolute superlative degree.
un aventura excellentissime 'a most excellent adventure'
The adjectives bon 'good', mal 'bad', magne 'great', and parve 'small' have optional irregular forms for the comparative and superlative.
bon → plus bon → le plus bon
or
bon → melior → optime
mal → plus mal → le plus mal
or
mal → pejor → pessime
magne → plus magne → le plus magne
or
magne → major → maxime
parve → plus parve → le plus parve
or
parve → minor → minime
Theoretically, every adjective may serve as a pronoun referring to something expressed in a previous passage.
Adverbs
There are two types of adverbs, primary and secondary. Primary adverbs are a closed class of grammatical operators, such as quasi, 'almost'; jam, 'already'; and totevia, 'anyway'. Secondary adverbs are an open class derived from corresponding adjectives by adding the suffix -mente (-amente after final -c).
felice 'happy' → felicemente 'happily'
magic 'magical' → magicamente 'magically'
A few common adverbs have optional short forms in -o.
sol 'alone' → solo or solmente 'only'
Like adjectives, adverbs use plus and minus to express the comparative and le plus and le minus to express the superlative.
Illa canta plus bellemente que illa parla. 'She sings more beautifully than she speaks.'
Le gepardo curre le plus rapide de omne animales. 'The cheetah runs the fastest of all animals.'
The adverbs equivalent to bon, 'good' and mal, 'bad' have optional irregular forms.
Deo adjuta les, qui se adjuta. 'God helps those who help themselves'.
Io me sibila un melodia. 'I whistle a tune to myself.'
Tu te rasava? 'Have you shaved?'
Francese se parla in Francia. 'French is spoken in France.'
The genitive case indicates possession (mi auto, 'my car'). The longer forms mie, tue etc. are adjectives, used in constructions like le auto es le mie, 'the car is mine'. They can also directly modify a noun.
alicun amicos mie 'some friends of mine'
Matre mie! Es un picante bolla de carne! 'Mamma mia, that's a spicy meatball!'
One could also assert the existence of a separate prepositional case, since third-person pronouns use the longer forms ille, illes etc. after a preposition in place of the expected le, les etc.
Da le can a illes. 'Give them the dog.'
Many users follow the European custom of using the plural forms vos etc. rather than tu etc. in formal situations.
Esque vos passava un viage placente, Seniora Chan? 'Did you have a pleasant trip, Mrs. Chan?'
Aperi vostre valise, Senior. 'Open your suitcase, Sir.'
Illes can be used as a sex-neutral pronoun, like English 'they'. Illas may be used for entirely female groups.
Impersonal pronouns
Il is an impersonal nominative pronoun used in constructions like il pluve, 'it's raining'. It can also serve as a placeholder when the true subject is a clause occurring later in the sentence. It may be omitted where the sense is clear.
Il deveni tarde. 'It's getting late.'
Il es ver que nos expende multe moneta. 'It's true that we're spending a lot of money.'
Es bon que vos veni ora. 'It's good that you come now.'
On is a nominative pronoun used when the identity of the subject is vague. The English translation is often 'one', 'you', or 'they'. It is sometimes equivalent to an English passive voice construction. The oblique form is uno.
On non vide tal cosas actualmente. 'One doesn't see such things these days.'
On sape nunquam lo que evenira. 'You never know what will happen.'
On construe un nove linea de metro al centro urban. 'They're building a new subway line to downtown.'
On collige le recyclabiles omne venerdi. 'Recyclables are picked up every Friday.'
Tal pensatas afflige uno in le profundo del depression. 'Such thoughts afflict one in the depths of depression.'
Demonstratives
Demonstratives
Role
Number
Gender
Proximate
Remote
Adjective
–
–
iste
ille
Pronoun
Sing.
masc.
iste
(ille)
fem.
ista
(illa)
neut.
isto
(illo)
Plur.
masc.
istes
(illes)
fem.
istas
(illas)
neut.
istos
(illos)
The main demonstratives are the adjective iste, 'this' and the corresponding pronouns iste (masculine), ista (feminine), and isto (neuter), which may be pluralized. They are used more widely than English 'this/these', often encroaching on the territory of English 'that/those'. Where the subject of a sentence has two plausible antecedents, iste (or one of its derivatives) refers to the second one.
Iste vino es pessime. 'This wine is terrible.'
Isto es un bon idea. 'That's a good idea.'
Janet accompaniava su soror al galleria... 'Janet accompanied her sister to the gallery...'
(a) Illa es un artista notabile. 'She [Janet] is a well-known artist.'
(b) Ista es un artista notabile. 'She [Janet's sister] is a well-known artist.'
The demonstrative of remoteness is ille 'that'. The corresponding pronouns ille, illa, illo and their plurals are identical with the third-person personal pronouns, though they are normally accentuated in speech.
Io cognosce ille viro; ille se appella Smith. 'I know that man; his name is Smith.'
Illo es un obra magnific. 'That is a magnificent work.'
Relative and interrogative pronouns
The relative pronouns for animates are qui (nominative case and after prepositions) and que (oblique case).
Nos vole un contabile qui sape contar. 'We want an accountant who knows how to count.'
Nos vole un contabile super qui nos pote contar. We want an accountant who we can count on.' (an accountant on whom we can count)
Nos vole un contabile que le policia non perseque. 'We want an accountant whom the police are not pursuing.'
For inanimates, que covers both the nominative and oblique cases.
Il ha duo sortas de inventiones: illos que on discoperi e illos que discoperi uno. 'There are two types of inventions: those that you discover and those that discover you.'
Cuje 'whose' is the genitive case for both animates and inanimates.
un autor cuje libros se vende in milliones 'an author whose books sell in the millions'
un insula cuje mysterios resta irresolvite 'an island whose mysteries remain unsolved'
All the above may be replaced by the relative adjective forms le qual (singular) and le quales (plural).
Mi scriptorio esseva in disordine – le qual, nota ben, es su stato normal. 'My desk was in a mess – which, mind you, is its usual state.'
Duo cosinos remote, del quales io sape nihil, veni visitar. 'Two distant cousins, of whom I know nothing, are coming to visit.'
The relative pronouns also serve as interrogative pronouns (see Questions).
The verb system is a simplified version of the systems found in English and the Romance languages. There is no imperfective aspect, as in Romance, no perfect as in English, and no continuous aspect, as in English and some Romance languages. Except (optionally) for esser 'to be', there are no personal inflections, and the indicative also covers the subjunctive and imperative moods. Three common verbs (esse, habe and vade) usually take short forms in the present tense (es, ha and va respectively), and a few optional irregular verbs are available.
For convenience' sake, this section often uses the term tense to also cover mood and aspect, though this is not strict grammatical terminology.
The table at the right shows the main verb forms, with examples for -ar, -er and -ir verbs (based on parlar 'to speak', vider 'to see', and audir 'to hear').
The simple past, future, and conditional tenses correspond to semantically identical compound tenses (composed of auxiliary verbs plus infinitives or past participles). These in turn furnish patterns for building more-complex tenses such as the future perfect.
Infinitives
Infinitive verbs always end in -ar, -er, or -ir. They cover the functions of both the infinitive and the gerund in English and can be pluralized where it makes sense.
Cognoscer nos es amar nos. 'To know us is to love us.'
Il es difficile determinar su strategia. 'It's hard to figure out his strategy.'
Illes time le venir del locustas. 'They fear the coming of the locusts.'
Le faceres de illa evocava un admiration general. 'Her doings evoked a widespread admiration.'
Infinitives are also used in some compound tenses (see below).
The present tense can be formed from the infinitive by removing the final -r. It covers the simple and continuous present tenses in English. The verbs esser 'to be', haber 'to have', and vader 'to go' normally take the short forms es, ha, and va rather than esse, habe, and vade.
Io ama mangos; io mangia un justo ora. 'I love mangoes; I'm eating one right now.'
Mi auto es vetere e ha multe defectos: naturalmente illo va mal! 'My car is old and has lots of things wrong with it: of course it runs poorly!'
The simple past tense can be formed by adding -va to the present tense form. It covers the English simple past and past perfect, along with their continuous equivalents.
Io vos diceva repetitemente: le hospites jam comenciava partir quando le casa se incendiava. 'I've told you again and again: the guests were already starting to leave when the house burst into flames.'
The simple future can be formed by adding -ra to the present tense form. Future tense forms are stressed on the suffix (retornara 'will return'). It covers the English simple and continuous future tenses.
Nos volara de hic venerdi vespere, e sabbato postmeridie nos prendera le sol al plagia in Santorini. 'We'll fly out Friday evening, and by Saturday afternoon we'll be sunbathing on the beach in Santorini.'
The simple conditional consists of the present tense form plus -rea. Like the future tense, it is stressed on the suffix (preferea 'would prefer). In function it resembles the English conditional.
Si ille faceva un melior reclamo, ille venderea le duple. 'If he did better advertising, he would sell twice as much.'
Participles
The present participle is effectively the present tense form plus -nte. Verbs in -ir take -iente rather than *-inte (nutrir 'to feed' → nutriente 'feeding'). It functions as an adjective or as the verb in a participial phrase.
un corvo parlante 'a talking crow'
Approximante le station, io sentiva un apprehension terribile. 'Approaching the station, I felt a sense of dread.'
The past participle can be constructed by adding -te to the present tense form, except that -er verbs go to -ite rather than *-ete (eder 'to edit' → edite 'edited'). It is used as an adjective and to form various compound tenses.
un conto ben contate 'a well told story'
Compound tenses
Three compound tenses – the compound past, future, and conditional – are semantically identical with the corresponding simple tenses.
The compound past tense consists of ha (the present tense of haber 'to have') plus the past participle.
Le imperio ha cadite. = Le imperio cadeva. 'The empire fell.'
The compound future tense is constructed from va (the present tense of vader 'to go') plus the infinitive.
Io va retornar. = Io retornara. 'I shall return.'
The rarely used compound conditional tense uses the auxiliary velle plus the infinitive.
Io velle preferer facer lo sol. = Io prefererea facer lo sol. 'I'd prefer to do it alone.'
The fourth basic compound tense is the passive, formed from es (the present tense of esser 'to be') plus the past participle.
Iste salsicias es fabricate per experte salsicieros. 'These sausages are made by expert sausage-makers.'
A wide variety of complex tenses can be created following the above patterns, by replacing ha, va, and es with other forms of haber, vader, and esser. Examples:
The future perfect, using habera 'will have' plus the past participle
Ante Natal, tu habera finite tu cursos. 'By Christmas you will have finished your courses.'
The past imperfect, using vadeva 'were going' plus the infinitive
Plus tarde illa vadeva scriber un romance premiate. 'Later she would write a prize-winning novel.'
Nostre planeta habeva essite surveliate durante multe annos. 'Our planet had been watched for many years.'
Other tenses
There are no distinct forms for the imperative and subjunctive moods, except in the case of esser 'to be'. Present-tense forms normally serve both functions. For clarity's sake, a nominative pronoun may be added after the verb.
Face lo ora! 'Do it now!'
Le imperatrice desira que ille attende su mandato. 'The empress desires that he await her command.'
Va tu retro al campo; resta vos alteros hic. 'You, go back to the camp; you others, stay here.'
The infinitive can serve as another, stylistically more impersonal, imperative form.
Cliccar hic. 'Click here.'
A less urgent version of imperative, the cohortative, employs a present-tense verb within a "that" ("que") clause and may be used with the first and third person as well as the second. The alternative vamos 'let's' (or 'let's go') is available for the second-person plural, but deprecated by some authorities.
Que tu va via! 'I wish you'd go away!'
Que illes mangia le brioche. 'Let them eat cake.'
Que nos resta hic ancora un die. or Vamos restar hic ancora un die. 'Let's stay here one more day.'
Sia is the imperative and subjunctive form of esser 'to be'. The regular form esse may also be used.
Sia caute! 'Be careful!'
Sia ille vive o sia ille morte... 'Be he alive or be he dead...'
Que lor vita insimul sia felice! 'May their life together be happy!'
Irregular verbs
Irregular forms of vader (ir)
Singular
Plural
1. pers.
2–3. pers.
Present
va
vamos
van
Past
iva
Future
ira
Conditional
irea
Imperative
i
Irregular forms of esser
Singular
Plural
1. pers.
2–3. pers.
1. pers.
2–3. pers.
Present
so
es
somos
son
Past
era
Future
sera
Conditional
serea
Imperative
sia
The only irregular verb forms employed by most users are es, ha, and va – the shortened present-tense forms of esser 'to be', haber 'to have' and vader 'to go' – plus sia, the imperative/subjunctive of esser.
Other irregular forms are available, but official Interlingua publications (and the majority of users) have always favoured the regular forms. These optional irregular forms are known as collaterals.
A significant minority of users employ certain collateral forms of esser 'to be': son (present plural), era (past), sera (future), and serea (conditional), instead of es,esseva,essera, and esserea.
Nos vancouveritas son un banda pittoresc. = Nos vancouveritas es un banda pittoresc. 'We Vancouverites are a colourful lot.'
Le timor era incognoscite. = Le timor esseva incognoscite. 'Fear was unknown.'
Que sera, sera. = Que essera, essera. 'What will be, will be.'
Il serea melior si nos non veniva. = Il esserea melior si nos non veniva. 'It would be better if we hadn't come.'
The forms io so 'I am', nos somos 'we are', nos vamos 'we go' and vos/illes van 'you/they go' also exist but are rarely used.
Double-stem verbs
The Neo-Latin vocabulary that underlies Interlingua includes a group of verbs whose stems mutate when attached to certain suffixes. For example, agente, agentia, actrice, activista, reagente, reaction are all derivatives of ager 'to act', but some use the primary stem ag-, while others use the secondary stem act-. There are hundreds of such verbs, especially in international scientific vocabulary.
This raises a logical issue. Adding -e to one of these secondary stems produces an adjective that is structurally and semantically equivalent to the past participle of the same verb. Experte, for example, is related to experir 'to experience', which has the past participle experite. Yet, semantically, there is little difference between un experte carpentero 'an expert carpenter' and un experite carpentero 'an experienced carpenter'. Effectively, experte = experite. Furthermore, one can form a word like le experito 'the experienced one' as a quasi-synonym of le experto 'the expert'.
This process can be reversed. That is, can one substitute experte for experite in compound tenses (and other second-stem adjectives for other past participles).
Io ha experte tal cosas antea. = Io ha experite tal cosas antea. 'I've experienced such things before.'
Illa ha scripte con un pluma. = Illa ha scribite con un pluma. 'She wrote with a quill.'
The original Interlingua grammar (Gode & Blair, 1951) permitted this usage, and illustrated it in one experimental text. A minority of Interlinguists employ the irregular roots, at least occasionally, more often with recognizable forms like scripte (for scribite 'written') than opaque ones like fisse (for findite 'split'). The practice is controversial. Deprecators suggest that they complicate the active use of Interlingua and may confuse beginners. Proponents argue that by using the irregular participles, students of Interlingua become more aware of the connections between words like agente and actor, consequentia and consecutive, and so on. A compromise position holds that the irregular forms may be useful in some educational contexts (e.g., when using Interlingua to teach international scientific vocabulary or as an intermediate step in the study of Romance languages), but not in general communication.
A similar issue concerns the present participles of caper 'to grasp, seize', facer 'to do, make', saper 'to know', and all verbs ending in -ciper, -ficer, and -jicer. The regular forms are facente, sapente, etc., but the "preferred forms", according to the original grammar, are faciente, sapiente, etc.
un homine sapiente = un homine sapente 'a knowledgeable person'
Recipiente le littera, ille grimassava. = Recipente le littera, ille grimassava. 'Receiving the letter, he grimaced.'
Today, most users employ the regular forms in spontaneous usage. Forms like sufficiente are often used as adjectives, under the influence of similar forms in the source languages.
Numerals
Cardinal numbers are formed by addition and multiplication of predetermined root numerals. Smaller values before larger ones corresponds to multiplication, while larger values before smaller ones corresponds to addition. Numerals below one hundred consist of a root numeral for the tens and a root numeral for the ones, concatenated with a hyphen, i.e. 42 quaranta-duo 'forty-two'.
For example, the number 2345 would be duo milles tres centos quaranta-cinque 'two thousand three hundred (and) forty-five', which corresponds to the expression 2 × 1000 + 3 × 100 + 40 + 5. The number 9 876 000 would be nove milliones octo centos septanta-sex milles 'nine million eight hundred (and) seventy-six thousand', which corresponds to the expression 9 × 1 000 000 + (8 × 100 + 70 + 6) × 1000. The conjunction e 'and' can always be inserted arbitrarily between any two roots in a number, even replacing the hyphen between tens and ones.
The cardinal numbers below 100 are all constructed regularly from nineteen roots. (Note that among the tens, fifty and onwards are constructed regularly from the corresponding ones and the ending -anta.)
0
zero
1
un
10
dece
2
duo
20
vinti
3
tres
30
trenta
4
quatro
40
quaranta
5
cinque
50
cinquanta
6
sex
60
sexanta
7
septe
70
septanta
8
octo
80
octanta
9
nove
90
novanta
The number 100 is cento 'hundred' and the number 1000 is mille 'thousand'. All further larger numbers follow the long scale.
100
cento
1 000
mille
1 000 0001
million
1 000 × 1 000 0001
milliardo
1 000 0002
billion
1 000 × 1 000 0002
billiardo
1 000 0003
trillion
1 000 × 1 000 0003
trilliardo
1 000 0004
quatrillion
1 000 × 1 000 0004
quatrilliardo
1 000 0005
quintillion
1 000 × 1 000 0005
quintilliardo
…
…
The ordinal numbers have their own root numerals for the ones (and ten).
1st
prime
2nd
secunde
3rd
tertie
4th
quarte
5th
quinte
6th
sexte
7th
septime
8th
octave
9th
none
10th
decime
last
ultime
All other ordinal numbers are formed by the cardinal number followed by the suffix -esime. In compound ordinals, only the last root numeral is modified.
11th
dece-prime 'eleventh'
102nd
cento secunde 'hundred (and) second'
99th
novanta-none 'ninety-ninth'
300th
tres centesime 'three hundredth'
Fractional, multiplicative, collective and adverbial numbers
With the exception of medie 'half', all fractional numerals are formed by a cardinal number representing the numerator followed by an ordinal number representing the denominator.
1/2
medie 'half'
1/4
un quarte 'one quarter'
22/7
vinti-duo septime 'twenty-two seventh(s)'
Multiplicative numerals consist of either 14 basic multiplicative numeral roots or 14 basic prefixes which can in principle be compounded to any word.
Multiplicative numeral
Multiplicative prefix
1
simple or simplice 'simple'
uni- or mono-
2
duple or duplice 'double'
bi- or di-
3
triple or triplice 'triple'
tri-
4
quadruple 'quadruple'
quadri- or tetra-
5
quintuple 'quintuple'
penta-
6
sextuple 'sixfold'
hexa-
7
septuple 'sevenfold'
hepta-
8
octuple 'eightfold'
octa-
9
nonuple 'ninefold'
ennea-
10
decuple 'tenfold'
deca-
100
centuple 'hundredfold'
hecto-
Continuing the series, all of the metric prefixes are valid productive prefixes in Interlingua. Beside these, there are also the irregular prefixes sesqui- 'one-and-a-half-', semi- 'half-', hemi- 'half-' and myria- 'ten-thousand-'.
All of the collective numerals are modelled after dozena 'dozen', and are formed by suffixing -ena to any cardinal numeral.
Numeric conventions
Decimals should always be written with commas by default, as per ISO recommendations. I.e. 3,1415 and not '3.1415' as in English. Since this would clash with the familiar usage of the comma as the thousands separator in English, this function is switched with the period in Interlingua, or alternatively empty spaces.
Ordinals and adverbials expressed in Arabic numerals are written as follows:
with the adverbials being identical except for ending in -o instead of -e. Alternatively, it is extremely common to simply use the suffixes -e or -o on their own for simplicity.
