Verbs Ending in -uir

Verbs whose infinitive ends in -uir form the largest of the vowel-stem -ir classes in European Portuguese. Unlike the small -air family (three base verbs plus a handful of compounds), -uir verbs fill two full pages of any conjugation dictionary: construir, destruir, influir, constituir, contribuir, substituir, distribuir, atribuir, diminuir, possuir, incluir, concluir, excluir, fluir and many more. The pattern is close to -air in spirit — both classes have a stem that ends in a vowel, both mark hiatus with an accented í, and both insert a glide in the 1sg — but -uir has one live, still-unsettled feature that makes it genuinely worth studying separately: the 2sg and 3sg present indicative forms of construir, destruir and a few others have two accepted spellings in European Portuguese, and you will see both in print.

The core pattern — shared with -air

Take construir as the representative. Remove the -uir, and you are left with the stem constru-. Adding the regular -ir endings gives you a paradigm with the same three key features you saw in -air verbs:

1. The 1sg present inserts a glide: construo (the -u- of the stem plus the -o of the ending, pronounced as a diphthong).
2. Wherever the stem-final -u- and the ending -i- form a hiatus, the i takes an accent: construí, construíste, construímos, construíram.
3. Where they form a diphthong, no accent: construiu.

Construir (to build) — full paradigm

Present indicative — with the live variation

This is the form that deserves special care. Traditional European Portuguese grammar gives:

The traditional forms constróis, constrói, constroem — with the stem vowel lowering from u to o and with a circumflex-type stress on the ó — reflect an older European Portuguese pattern shared with sair (sais, sai, saem). The alternative forms construis, construi, construem keep the stem u throughout and are the outcome of a slow regularization that is now widespread, especially in younger speakers and colloquial registers. Both forms are attested in modern edited prose; good PT-PT dictionaries list them as co-existing variants.

For learners, the practical advice is: learn the traditional forms (constróis, constrói, constroem), because they are what you will see in formal writing and on exams, and be ready to recognize the alternative forms when you hear them in speech. Both are grammatical; neither is wrong.

The same alternation applies to destruir (destróis/destruis, destrói/destrui, destroem/destruem) and to reconstruir. It does not apply to most other -uir verbs, which only have the traditional u-preserving forms: influis, influi, influem (not *infloi), contribuis, contribui, contribuem (not *contróis). The o↔u alternation is limited to the construir / destruir family.

Preterite

Same principle as sair: every form takes the accented í except the 3sg construiu, which is a diphthong (cons-tru-IU). The 1pl construímos is identical in spelling to the 1pl present — context decides.

Imperfect

All imperfect forms are hiatus and take the accent.

Future and conditional

In the future and conditional, the full infinitive construir is preserved as the stem, and the -ui- within it is pronounced as a diphthong, so no accent is needed — except in the 1pl conditional construiríamos, where the -í- of the ending is stressed.

Present subjunctive

Built on the 1sg indicative stem constru- plus the -a endings. The -ua- is a diphthong, so no accent.

Imperfect subjunctive

Construísse, construísses, construísse, construíssemos, construíssem — all hiatus, all accented.

The -uir family — organized by meaning

The class is large and includes some of the most frequently used verbs in written Portuguese. A mini-taxonomy:

Building and destroying: construir, destruir, reconstruir

Adding and subtracting: incluir, excluir, concluir

Contributing and distributing: contribuir, distribuir, substituir, atribuir

Having and possessing: possuir, constituir

Possuir is formal; in everyday speech speakers use ter (esta casa tem vistas...). Possuir dominates in legal and real-estate language.

Decreasing and flowing: diminuir, fluir, influir

A comprehensive reference table

Note that only construir, destruir, reconstruir show the o↔u alternation. For every other verb in the class, the 3sg is simply -ui with no vowel change.

Why the construir/destruir alternation exists

A brief historical note for the curious. The traditional forms constrói, destrói come from an older pattern in which the stem vowel u lowered to o when stressed — a pattern also visible in archaic forms of other verbs (saúde → soúde in some old texts, though modern Portuguese has settled on saúde). In construir, destruir this lowering survived into modern European Portuguese, giving constrói. However, by analogy with the rest of the -uir class (where no such lowering occurs — influi, contribui, incluí), speakers have gradually regularized construir towards construi. As of 2026, both forms are current in PT-PT; prescriptive grammars and dictionaries accept both.

Brazilian Portuguese has gone further and typically accepts both forms too, but the alternative construi/destrui is more common in everyday speech there.

Past participle and gerund

All -uir verbs have past participles with the accented í (hiatus): construído, destruído, influído, contribuído, incluído, concluído, possuído, diminuído. The gerunds do not have the accent, because the -ui- is a diphthong: construindo, destruindo, influindo, contribuindo, incluindo, concluindo.

Irregular participle alert: incluir has a dual past participle — the regular incluído for the compound tenses with ter/haver (tenho incluído), and the short form incluso used adjectivally and with ser/estar (está incluso no preço). Similarly: excluir → excluído / excluso, concluir → concluído / concluso. This pattern (dual participles, one for the auxiliary ter, one for ser/estar) is shared by a number of Portuguese verbs.

The imperative

Following the general pattern:

• Affirmative tu = 3sg present indicative. So constrói (traditional) or construi (alternative), destrói / destrui, inclui, conclui, contribui, substitui.
• Negative tu / affirmative and negative você / vocês = present subjunctive. So (não) construas, construa, construam, etc.

Spanish comparison

Spanish has many cognates: construir, destruir, contribuir, incluir, concluir, distribuir, sustituir, disminuir. The paradigms are generally similar, but with some key differences:

• Spanish inserts a y in the glide position: construyo, construyes, construye, construimos, construyen. Portuguese inserts no consonant: construo, constróis, constrói, construímos, constroem.
• Spanish accents the hiatus í in a similar way in the preterite (construí, construiste, construyó... — though the accent pattern differs from Portuguese).
• Spanish has no alternation between construyo and *constroyo — the u is preserved throughout. The Portuguese o↔u alternation in the construir family is a PT-specific feature.

If you know Spanish y-insertion, be careful not to transfer it: Portuguese construo has no y.

English comparison

English has no verb-class system like this. The nearest analogue to understanding construir is that English build / built / built changes vowels in a strong-verb pattern, but English has no paradigm-internal vowel alternation between persons (we don't say I build / you bield / he boald). The Portuguese distinction between construo (1sg) and constrói (3sg) is alien to English thinking, but it is just Portuguese faithfully recording a pronunciation difference that English would gloss over.

Common Mistakes

The 1sg of -uir verbs ends in -uo (diphthong), not -uio.

Both constrói and construi are accepted in contemporary PT-PT; constrói is the form favoured in formal writing and traditional grammars. If in doubt, use constrói.

Both present and preterite 1pl of construir are spelled construímos. The accent is obligatory.

Portuguese does not insert a y between stem vowel and ending.

With ter/haver use the regular participle (incluído). The short form (incluso) appears with ser/estar and in adjectival uses.

Key takeaways

• The -uir class is large and regular: construir, destruir, influir, contribuir, incluir, concluir, distribuir, diminuir, possuir, fluir and many others.
• The pattern mirrors the -air class: 1sg insert glide (construo), hiatus forms take accented í (construí, construíste, construímos, construíram, construía, construído), diphthongs take no accent (construiu, construindo, construa).
• Construir, destruir, reconstruir have a live alternation in 2sg, 3sg and 3pl of the present indicative: traditional constróis, constrói, constroem versus modern construis, construi, construem. Both are accepted in modern European Portuguese.
• Incluir, excluir, concluir have dual past participles: regular incluído for compound tenses, short incluso for adjectival/ser-estar uses.
• Do not insert a Spanish y (*construyo). Portuguese keeps the glide implicit.
• Do not forget the accent on hiatus í — it is orthographically required.