Stem-Changing -ir Verbs | Portuguese (Brazil) Grammar

A big group of common -ir verbs look irregular but are actually following one of the most reliable patterns in Portuguese. In the eu form of the present indicative, the stem vowel raises: e becomes i, and o becomes u. So preferir gives prefiro, and dormir gives durmo. Learn the logic once and you unlock dozens of verbs at no extra cost.

Why this happens

This is a phonetic echo of the verb's own history, but you don't need the history to predict it — you need the trigger. The shift appears specifically in the eu form of the present indicative (and, as we'll see, throughout the present subjunctive). In every other present-indicative person, the stem keeps the vowel of the infinitive.

Think of it as: the eu form raises the vowel, and everyone else leaves it alone.

💡

This is the single most cost-effective irregular pattern in Brazilian Portuguese. Unlike truly irregular verbs (ser, ir, ter) that you must memorize one by one, here a single rule — raise the eu-form vowel — covers a whole shelf of everyday verbs.

Pattern 1: e → i

When the last stem vowel is e, it becomes i in the eu form. Take preferir (to prefer): drop -ir to get prefer-, raise the e to i in the eu form, and you get prefiro.

Subject	preferir	sentir	servir
eu	prefiro	sinto	sirvo
você / ele / ela	prefere	sente	serve
nós	preferimos	sentimos	servimos
vocês / eles / elas	preferem	sentem	servem

Other verbs in this group: repetir → repito, vestir → visto, mentir → minto, seguir → sigo, competir → compito.

Eu prefiro café, mas ela prefere chá de manhã.

I prefer coffee, but she prefers tea in the morning.

Eu sinto muito pela sua perda.

I'm very sorry for your loss.

Eu visto o uniforme só quando tem reunião.

I wear the uniform only when there's a meeting.

Notice how clean the contrast is: eu sinto but você sente; eu visto but ela veste. The vowel raises only for eu.

Pattern 2: o → u

When the last stem vowel is o, it becomes u in the eu form. The model is dormir (to sleep): dorm- → durmo.

Subject	dormir	cobrir	engolir
eu	durmo	cubro	engulo
você / ele / ela	dorme	cobre	engole
nós	dormimos	cobrimos	engolimos
vocês / eles / elas	dormem	cobrem	engolem

Other verbs in this group: descobrir → descubro, tossir → tusso, cobrir → cubro.

Eu durmo com a janela aberta o ano inteiro.

I sleep with the window open all year round.

Sempre que eu descubro um restaurante novo, eu te aviso.

Whenever I discover a new restaurant, I'll let you know.

Eu engulo o remédio com água, não consigo sem.

I swallow the pill with water; I can't do it without.

Pattern 3: the subir / fugir group

This third group is a twist on the first two, and it surprises learners because the change appears where you don't expect it. In verbs like subir (to go up) and fugir (to flee), the eu form actually keeps the higher vowel of the infinitive, while it is the você/ele and vocês/eles forms that lower it.

Subject	subir	fugir	sumir
eu	subo	fujo	sumo
você / ele / ela	sobe	foge	some
nós	subimos	fugimos	sumimos
vocês / eles / elas	sobem	fogem	somem

So eu subo (with u) but ele sobe (with o); eu fujo but ela foge. The high vowel survives in the eu and nós forms; the singular and plural third persons lower it to o. (The fugir spelling also flips g→j before the o of fujo to keep the soft sound — a spelling rule, not a stem change.) Other members: acudir, cuspir → cuspo / cospe.

Eu subo a pé, mas ela sobe de elevador.

I go up on foot, but she takes the elevator up.

Eu sempre fujo dessas conversas, mas o João nunca foge.

I always run from those conversations, but João never does.

The change spreads to the whole present subjunctive

Here is the payoff. The vowel that shows up in the eu form is the vowel that the present subjunctive uses in every person. The subjunctive is built off the eu present-indicative stem, so it inherits the raised vowel across the board.

Subject	preferir (subjunctive)	dormir (subjunctive)
que eu	prefira	durma
que você / ele	prefira	durma
que nós	prefiramos	durmamos
que vocês / eles	prefiram	durmam

Espero que você durma bem hoje à noite.

I hope you sleep well tonight.

É melhor que a gente prefira a verdade, por mais dura que seja.

It's better that we prefer the truth, however hard it may be.

So the durmo you learn today is also the durma of the subjunctive — one stem, two payoffs. For the full mechanics, see present subjunctive: -er and -ir formation.

💡

English has nothing like this. Our verbs do change vowels in irregular pasts (sing → sang, ring → rang), but never to mark the first person of the present. To an English speaker, "I sleep / he sleeps" feels rock-stable, so durmo vs dorme feels arbitrary. It isn't — it's the same vowel-raising rule applied consistently.

Common mistakes

❌ Eu dormo oito horas por noite.

Incorrect — dormir raises o→u in the eu form.

✅ Eu durmo oito horas por noite.

I sleep eight hours a night.

❌ Eu prefero ficar em casa hoje.

Incorrect — preferir raises e→i in the eu form.

✅ Eu prefiro ficar em casa hoje.

I prefer to stay home today.

❌ Eu sobo a escada toda manhã.

Incorrect — subir keeps u in the eu form: subo.

✅ Eu subo a escada toda manhã.

I go up the stairs every morning.

❌ Nós prefirimos chá.

Incorrect — the change does NOT touch the nós present-indicative form; it stays regular.

✅ Nós preferimos chá.

We prefer tea.

❌ Eu fugo do trânsito sempre que posso.

Incorrect — fugir's eu form is fujo (g→j spelling before o).

✅ Eu fujo do trânsito sempre que posso.

I avoid the traffic whenever I can.

Key takeaways

The shift happens only in the eu present-indicative form: e→i, o→u.
All other present-indicative persons keep the infinitive vowel — except the subir/fugir group, where the singular and plural third persons lower the vowel instead.
The raised vowel reappears across all persons of the present subjunctive.
It is a rule, not a list — once you internalize "raise the eu vowel," you can predict the eu form of verbs you've never met.

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