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" and indefinite article is "un". They are invariable and are used roughly as in English. The prepositions "a" ("to") and "de" ("of") can optionally be fused with "le" into "al" and "del" respectively.
Nouns.
Nouns inflect for number only. Plural nouns take "-s" after a vowel, "-es" after a consonant (but final "-c" changes in spelling to "-ches" to preserve the sound of "c").
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".
These colour the regular forms as masculine when they appear in the same context.
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.
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.
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").
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.
Pronouns.
Personal pronouns.
Personal pronouns inflect for number, case, and (in the third person) gender.
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.
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.
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.
"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".
Demonstratives.
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.
Relative and interrogative pronouns.
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).
Verbs.
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.
Infinitives are also used in some compound tenses (see below).
Simple tenses.
There are four simple tenses: the present, past, future, and conditional.
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.
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.
Compound tenses.
Three compound tenses – the compound past, future, and conditional – are semantically identical with the corresponding simple 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:
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.
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.
Irregular verbs.
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".
The forms "io so" 'I am' and "nos somos" 'we are' also exist but are rarely used.
Double-stem verbs.
The Neolatin 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).
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.
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.
Syntax.
The normal word order in Interlingua is subject–verb–object, though this may be relaxed where the sense is clear.
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.
Questions.
Questions can be created in several ways, familiar to French speakers.