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.
Grammatical features absent from any of the primary control languages (English, French, Italian, Spanish and Portuguese) were dropped.
Finite verbs virtually always end in -a, -e, or -i, while infinitives add -r: scribe, 'write', 'writes'; scriber, 'to write'.
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.
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).
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.
The adjectives bon 'good', mal 'bad', magne 'great', and parve 'small' have optional irregular forms for the comparative and superlative.
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).
Except (optionally) for esser 'to be', there are no personal inflections, and the indicative also covers the subjunctive and imperative moods.
For convenience' sake, this section often uses the term tense to also cover mood and aspect, though this is not strict grammatical terminology.
They cover the functions of both the infinitive and the gerund in English and can be pluralized where it makes sense.
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: There are no distinct forms for the imperative and subjunctive moods, except in the case of esser 'to be'.
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.
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 Neo-Latin vocabulary that underlies Interlingua includes a group of verbs whose stems mutate when attached to certain suffixes.
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.
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').
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.
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.
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.
