E-to-I Stem-Changing Verbs

A large and extremely useful family of European Portuguese verbs belongs to the e-to-i stem-changing class. These are -ir verbs whose stem contains the vowel e, and whose stem raises that e to i in a strictly defined set of forms: the first-person singular of the present indicative, and every person of the present subjunctive. Everything else about them is regular. Once you recognize the pattern, you can conjugate servir, vestir, mentir, sentir, preferir, seguir, conseguir, repetir and several dozen others with confidence.

The core pattern

The change is small but consequential. Take the infinitive, remove the -ir, and look at the stem vowel. If it is an e followed by a consonant, the verb almost always belongs to this class. The vowel behaves like this:

• In the forms where the stem is stressed and the vowel is specifically eu — it rises to i.
• In every other present indicative form — it stays e.
• Throughout the present subjunctive — it is i.

The logic is phonological, not arbitrary. In European Portuguese, the unstressed 1sg subjunctive ending -a and the indicative -o both raise a preceding high-mid e by one vowel step. The other present indicative forms (-es, -e, -imos, -em) preserve the original mid vowel, so the stem stays as you would expect from the infinitive.

Servir (to serve) — full paradigm

Notice how the indicative and subjunctive eu forms are spelled identically (sirvo / sirva) — both have the raised i. The difference between them is the ending (-o vs -a), not the stem. In the tu, ele and eles forms, the two moods diverge more obviously: indicative keeps the e (serves, serve, servem), while the subjunctive raises it (sirvas, sirva, sirvam).

Vestir (to dress / to wear)

Vestir is almost always used reflexively when it means "to get dressed" (vestir-se), and transitively when you are putting something on or putting clothes on someone else (vestir o casaco, vestir a filha).

Mentir (to lie / to tell a lie)

Sentir (to feel)

The fixed expression sinto muito (literally "I feel a lot") is the standard condolence in Portuguese — note that it uses the stem-changed 1sg.

Preferir (to prefer)

Seguir (to follow) and its compounds

Seguir combines the e-to-i vowel change with a small orthographic adjustment: the gu of the infinitive loses its silent u before o or a to keep the hard g sound. So the eu form is sigo, not seguo, and the subjunctive is siga, sigas, siga, sigamos, sigam.

The compounds behave identically: conseguir (to manage / to achieve — consigo, consegues, consegue, conseguimos, conseguem), perseguir (to chase / to pursue — persigo, persegues...), and prosseguir (to proceed — prossigo, prossegues...).

Repetir (to repeat)

Divertir (to amuse) and more

The same pattern extends to a cluster of less frequent but still useful verbs: divertir (divirto, divertes, diverte, divertimos, divertem; subj. divirta), aderir (adiro, aderes, adere...; subj. adira), ferir (to wound — firo, feres...; subj. fira), refletir (reflito, refletes...; subj. reflita), competir (compito, competes...; subj. compita), and concorrer is not in this class because it is -er, but its cousin progredir (progrido, progredes...) is.

The imperative — a subtle trap

The imperative is where learners most often slip. European Portuguese builds commands as follows:

• Affirmative tu = the 3rd-person singular present indicative (no stem change: serve!, veste!, mente!, sente!, prefere!, segue!, repete!).
• Affirmative você / vocês and every negative imperative = the corresponding present subjunctive form (stem-changed: sirva!, vista!, minta!, sinta!, prefira!, siga!, repita! and não sirvas!, não vistas!, não mintas! etc.).

This means that the same verb can appear with the unchanged stem in a positive tu command and with the changed stem in a negative tu command — only a few letters apart:

How this compares to Spanish

If you know Spanish, a side-by-side view makes the Portuguese pattern easier to grasp — and easier to keep separate:

The key contrast: Spanish splits verbs into e→ie (sentir, preferir, mentir), e→i (servir, vestir, seguir, repetir, pedir), o→ue (dormir), and o→u (morir). Portuguese collapses all the front-vowel verbs into one class (e→i) and all the back-vowel verbs into one class (o→u). If a verb alternates in Spanish at all, it almost certainly alternates in Portuguese — but always by simple raising, never by diphthongization.

English-speakers' angle

English has no stem-changing system at all — the closest comparison is strong verbs like sing / sang / sung, where a root vowel shifts between tenses, not between persons of the same tense. The idea that I should say sirvo but you should say serves, with no analogous shift in English, takes getting used to. The payoff is that once you internalize the boot-shaped pattern, you will have conjugated the majority of common -ir verbs correctly — this one class covers a surprising share of what you need day-to-day.

Common Mistakes

Key takeaways

The e-to-i class is one of the most productive and everyday patterns in European Portuguese. Master the boot: the 1sg indicative and every subjunctive form raise the stem vowel; every other present indicative form keeps it. The imperative inherits this asymmetry — affirmative tu uses the unchanged stem, negative tu uses the changed one. No other tense or mood is affected, so once you have these two paradigms locked in, the rest of each verb is fully regular.