# Interlingua grammar

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/Portuguese gatos 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'.

## Articles

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, -g change in spelling to -ches, -ghes to preserve the hard [k] and [g] 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, where the two nouns refer to the same thing.
    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.
    bonmente → plus bonmente → le plus bonmente or ben → plus ben → le plus ben or ben → melio → optimo malmente → plus malmente→ le plus malmente or mal → plus mal → le plus mal or mal → pejo → pessimo

## Pronouns
### Personal pronouns

Personal pronouns – singular :
| Person | Gender | Nom. | Pre. | Obl. | Refl. | Genitive |
| First | – | io, yo$^*$, ego$^*$ | me | me | me | mi, mie |
| Second | – | tu | te | te | te | tu, tue |
| Third | masc. | ille | ille | le | se | su, sue |
| Third | fem. | illa | illa | la | se | su, sue |
| Third | neut. | illo | illo | lo | se | su, sue |
| *Yo and ego are rarely used. Ego comes from words like egoismo, egoista, yo is likely a borrowing from Occidental. |||||||
| Personal pronouns – plural |||||||
| Person | Gender | Nom. | Pre. | Obl. | Refl. | Genitive |
| First | – | nos | nos | nos | nos | nostre |
| Second | – | vos | vos | vos | vos | vostre |
| Third | masc. | illes | illes | les | se | lor, lore |
| Third | fem. | illas | illas | las | se | lor, lore |
| Third | neut. | illos | illos | los | se | lor, lore |
Personal pronouns inflect for number, case, and (in the third person) gender.
* The nominative case is the default form and typically serves as the subject of a verb.
       "Qui es ibi?" "Io." "Who's there?" "Me."
       Tu arrestava le chef de policia. 'You have arrested the chief of police.'
* The oblique case is used for direct objects, and may also be used for indirect objects. (Alternatively, indirect objects are expressed through a, 'to' plus a pronoun.)
       Le caffe es excellente: proba lo! 'The coffee is excellent: try it!'
       Dice me le conto; dice me lo (or Dice le conto a me...) 'Tell me the story; tell it to me.'
* Reflexive pronouns are used when the subject of a verb is identical with the direct or indirect object. As in the Romance languages, reflexive constructions are often used where English would employ an intransitive verb or the passive voice.
       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) |
| Pronoun | Sing. | fem. | ista | (illa) |
| Pronoun | Sing. | neut. | isto | (illo) |
| Pronoun | Plur. | masc. | istes | (illes) |
| Pronoun | Plur. | fem. | istas | (illas) |
| Pronoun | Plur. | 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).

## Verbs

Main verb forms :
| Tense | Ending | -ar verbs | -er verbs | -ir verbs |
| Infinitive | -r | parlar | vider | audir |
| Present | – | parla | vide | audi |
| Past* | -va | parlava | videva | audiva |
| Future* | -ra | parlara | videra | audira |
| Conditional* | -rea | parlarea | viderea | audirea |
| Present participle | -(e)nte | parlante | vidente | audiente |
| Past participle | -te | parlate | vidite | audite |
| *For alternative, compound forms, see Compound tenses. ||||||
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).

### Simple tenses

There are four simple tenses: the present, past, future, and conditional.
* 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.'
* The passive-voice past perfect, using habeva essite 'had been' plus the past participle
       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 | Singular | Singular | Plural | Plural | Plural |
| | Singular | Singular | Singular | 1. pers. | 2–3. pers. | 2–3. pers. |
| Present | va | va | va | vamos | van | van |
| Past | iva | iva | iva | iva | iva | iva |
| Future | ira | ira | ira | ira | ira | ira |
| Conditional | irea | irea | irea | irea | irea | irea |
| Imperative | i | i | i | i | i | i |
Irregular forms of esser :
| | Singular | Singular | Singular | Plural | Plural | Plural |
| | 1. pers. | 2–3. pers. | 2–3. pers. | 1. pers. | 2–3. pers. | 2–3. pers. |
| Present | so | es | es | somos | son | son |
| Past | era | era | era | era | era | era |
| Future | sera | sera | sera | sera | sera | sera |
| Conditional | serea | serea | serea | serea | serea | serea |
| Imperative | sia | sia | sia | sia | sia | 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.
    sentir 'to feel' (second stem: sens-) → sentimento, sensor
    repeller 'to push away' (second stem: repuls-) → repellente, repulsive
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.)
    0zero 1un10dece 2duo20vinti 3tres30trenta 4quatro40quaranta 5cinque50cinquanta 6sex60sexanta 7septe70septanta 8octo80octanta 9nove90novanta
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 1 000 000$^1$million 1 000 × 1 000 000$^1$milliardo 1 000 000$^2$billion 1 000 × 1 000 000$^2$billiardo 1 000 000$^3$trillion 1 000 × 1 000 000$^3$trilliardo 1 000 000$^4$quatrillion 1 000 × 1 000 000$^4$quatrilliardo 1 000 000$^5$quintillion 1 000 × 1 000 000$^5$quintilliardo ……
The ordinal numbers have their own root numerals for the ones (and ten).
    1stprime 2ndsecunde 3rdtertie 4thquarte 5thquinte 6thsexte 7thseptime 8thoctave 9thnone 10thdecime lastultime
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.
    11thdece-prime 'eleventh' 102ndcento secunde 'hundred (and) second' 99thnovanta-none 'ninety-ninth' 300thtres 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.
    1/2medie 'half' 1/4un quarte 'one quarter' 22/7vinti-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 numeralMultiplicative prefix 1simple or simplice 'simple'uni- or mono- 2duple or duplice 'double'bi- or di- 3triple or triplice 'triple'tri- 4quadruple 'quadruple'quadri- or tetra- 5quintuple 'quintuple'penta- 6sextuple 'sixfold'hexa- 7septuple 'sevenfold'hepta- 8octuple 'eightfold'octa- 9nonuple 'ninefold'ennea- 10decuple 'tenfold'deca- 100centuple '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:
    1me '1st', 2nde '2nd', 3tie '3rd', 4te '4th', 5te '5th', 6te '6th', 7me '7th', 8ve '8th', 9ne '9th', 10me '10th', 20me '20th', 100me '100th', etc.
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.

## Syntax

The normal word order in Interlingua is subject–verb–object, though this may be relaxed where the sense is clear.
    Ille reface horologios. 'He fixes clocks.'
    Amandolos ama io tanto, io comprava un amandoliera. 'I love almonds so much, I bought an almond orchard.'
Pronouns, however, tend to follow the Romance pattern subject–object–verb, except for infinitives and imperatives, where the object follows the verb.
    Ille los reface. 'He fixes them.'
    Nos vole obtener lo. 'We want to get it.'
    Jecta lo via! 'Throw it away!'
When two pronouns, one a direct and one an indirect object, occur with the same verb, the indirect object comes first.
    Io les lo inviava per avion. 'I sent it to them by air.'
    Io la los inviava per nave. 'I sent them to her by ship.'
The position of adverbs and adverbial phrases is similar to English.

### Questions

Questions can be created in several ways, familiar to French speakers.
* By reversing the position of the subject and verb.
       Ha ille arrivate? 'Has he arrived?'
       Cognosce tu ben Barcelona? 'Do you know Barcelona well?'
       Te place le filmes de Quentin Tarantino? 'Do you like the films of Quentin Tarantino?'
* By replacing the subject with an interrogative word.
       Qui ha dicite isto? 'Who said this?'
       "Que cadeva super te?" "Un incude." '"What fell on you?" "An anvil."'
* For questions that can be answered with 'yes' or 'no', by adding the particle esque (or rarer an) to the start of the sentence.
       Esque illa vermente lassava su fortuna a su catto? (or An illa...) 'Did she really leave her fortune to her cat?'
* By changing the intonation or adding a question mark, while keeping the normal word order.
       Tu jam ha finite tu labores? 'You finished your work yet?'