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. For modern trends, see Variants.
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 control languages were dropped. For example, there is neither adjectival agreement (Spanish 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.
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 -e 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'.
Interlingua has no grammatical gender. Animate nouns are sex-neutral, unless they refer to a male or a female. Thus, jornalista 'journalist' and scientifico '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.
These colour the regular forms as masculine when they appear in the same context.
An adjective never has to agree with the noun it modifies, but adjectives may be pluralized when there is no explicit noun to modify.
Comparative degree is expressed by plus or minus preceding the adjective and superlative degree by le plus or le minus.
The suffix -issime may be used to express the absolute superlative degree.
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|
A few common adverbs have optional short forms in -o.
Like adjectives, adverbs use plus and minus to express the comparative and le plus and le minus to express the superlative.
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|
|Personal pronouns – singular|
|Personal pronouns – plural|
Personal pronouns inflect for number, case, and (in the third person) gender.
One could also claim 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.
Many users follow the European custom of using the plural forms vos etc. rather than tu etc. in formal situations.
Illes can be used as a sex-neutral pronoun, like English 'they'. Illas may be used for entirely female groups.
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.
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.
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.
The relative pronouns for animates are qui (nominative case and after prepositions) and que (oblique case).
For inanimates, que covers both the nominative and oblique cases.
Cuje 'whose' is the genitive case for both animates and inanimates.
All the above may be replaced by the relative adjective forms le qual (singular) and le quales (plural).
The relative pronouns also serve as interrogative pronouns (see Questions).
|Main verb forms|
|Tense||Ending||-ar verbs||-er verbs||-ir verbs|
|*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 aspect 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 usually take short forms in the present tense, and a few optional irregular verbs are available (though little used).
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 are also used in some compound tenses (see below).
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.
The fourth basic compound tense is the passive, formed from es (the present tense of esser 'to be') plus the past participle.
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 infinitive can serve as another, stylistically more impersonal, imperative form.
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.
Sia is the imperative and subjunctive form of esser 'to be'. The regular form esse may also be used.
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.
The forms io so 'I am' and nos somos 'we are' also exist but are rarely used.
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'.
Arguably, 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).
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 the International Scientific Vocabulary), but not in general communication.
A similar issue concerns the present participles of caper 'to take', facer 'to 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.
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.
Pronouns, however, tend to follow the Romance pattern Subject–Object–Verb, except for infinitives and imperatives, where the object follows the verb.
When two pronouns, one a direct and one an indirect object, occur with the same verb, the indirect object comes first.
The position of adverbs and adverbial phrases is similar to English.