The plain Class IV verbs — a dormi, a veni, a fugi — take the endings — / -i / -e / -im / -iți / — (-u). But just like Class I, a band of these verbs diphthongize the stem vowel when the third-person ending throws the stress onto the stem. A dormi (to sleep) is not el dorme — it is el doarme. This page covers the three stem alternations you meet in Class IV (o→oa, e→ie, a→ă) and, just as importantly, draws the dividing line between these and the -esc verbs, which famously never diphthongize because the stressed infix soaks up the stress.
The same stress rule, a different class
The logic is identical to Class I stem changes: when the ending is unstressed (in the singular and 3pl), the stress sits on the stem vowel, and a stressed mid vowel breaks into a diphthong. When the ending is stressed (noi -im, voi -iți), the stem reverts to plain. So once again the alternation clusters in the 3sg and 3pl and vanishes in noi/voi. The defining example is a dormi:
| Person | Form | Stem vowel | Why |
|---|---|---|---|
| eu | dorm | o | bare stem keeps plain o |
| tu | dormi | o | front -i, no diphthong |
| el / ea | doarme | oa | stem stressed before -e → o breaks to oa |
| noi | dormim | o | ending stressed → stem stays plain |
| voi | dormiți | o | ending stressed → stem stays plain |
| ei / ele | dorm | o | = eu, bare stem, plain o |
There is a subtle but important contrast with Class I here. In Class I the diphthong appears before the back-vowel ending -ă (3sg and 3pl: pleacă). In plain Class IV the 3pl is the bare stem (ei dorm, = eu), so the diphthong shows up only in the 3sg before -e (doarme), and the 3pl stays plain. Watch this — it is the opposite distribution of Class I in the third-person plural.
Dorm prost când e prea cald în cameră.
I sleep badly when the room is too hot.
Copilul doarme dus, nu-l trezi.
The child is fast asleep, don't wake him.
Ei dorm la bunici în weekend.
They sleep at their grandparents' on weekends. (3pl = bare stem dorm)
o → oa: a dormi, a coborî, a muri
The most common Class IV diphthong. Note that the -î verb a coborî (to go down, to get off) works the same way, with the back-vowel diphthong in the third person.
| Infinitive | eu | tu | el / ea | noi | ei / ele |
|---|---|---|---|---|---|
| a dormi (to sleep) | dorm | dormi | doarme | dormim | dorm |
| a coborî (to descend) | cobor | cobori | coboară | coborâm | coboară |
| a muri (to die) | mor | mori | moare | murim | mor |
A useful wrinkle: a coborî is an -î verb, so its 3pl is coboară (not a bare stem like dorm), patterning more like Class I in the third-person plural. And a muri shows an extra reduction — o→u in the unstressed noi/voi (murim, muriți) on top of the o→oa diphthong in the third person (moare).
Cobor la următoarea stație, mulțumesc.
I'm getting off at the next stop, thanks.
Trenul coboară încet spre vale.
The train descends slowly toward the valley.
Florile mor fără apă în câteva zile.
The flowers die without water in a few days.
e → ie: a ieși and the fronted diphthong
A stressed e in a Class IV stem can break into ie (a slightly different diphthong from Class I's ea). The clearest everyday example is in verbs where the stem e is stressed in the third person.
| Infinitive | eu | tu | el / ea | noi | ei / ele |
|---|---|---|---|---|---|
| a ieși (to go out, to exit) | ies | ieși | iese | ieșim | ies |
| a pieri (to perish) | pier | pieri | piere | pierim | pier |
These verbs already carry the ie in every form because the stem itself begins with the diphthong — a ieși is built on an ie- stem throughout (ies, ieși, iese, ieșim). The point to absorb is that the ie is a genuine diphthong, not two separate vowels, and it does not collapse to plain e the way an unstressed ea would.
Ies la o cafea cu colegii după muncă.
I'm going out for a coffee with colleagues after work.
La ce oră iese din tură?
What time does he get off shift?
Ieșim în oraș diseară, vii și tu?
We're going out tonight, are you coming too?
a → ă
The flattest alternation. A stressed a in the stem can surface as ă in some persons. It is less dramatic than the diphthongs but still trips up English speakers who freeze the infinitive vowel. You meet it in the interaction between the stem and the noi/voi endings of certain verbs.
Mă apropii încet de casă.
I'm slowly getting close to the house. (a se apropia — note the stem flexing)
Adresa nu se potrivește cu harta.
The address doesn't match the map. (a se potrivi)
Why -esc verbs never diphthongize
Here is the payoff that separates this page from the rest. The hugely common -esc subtype — a vorbi → vorbesc, a citi → citesc — looks like it should diphthongize too. It never does. The reason is mechanical: the -esc infix is stressed itself (vor-BESC, ci-TESC), so the stress lands on the infix, not on the stem vowel. With no stress on the stem, there is nothing to break into a diphthong. The stem just sits there.
| Stress lands on | 3sg | Diphthong? | |
|---|---|---|---|
| a dormi (plain) | the stem | doarme | yes — o→oa |
| a vorbi (-esc) | the infix | vorbește | no — stem inert |
This is exactly why you must learn, verb by verb, whether an -i verb is plain (and therefore can diphthongize) or takes -esc (and therefore cannot). A dormi and a vorbi look identical in the infinitive; only their behavior tells them apart.
El doarme, dar ea vorbește la telefon.
He's asleep, but she's on the phone. (doarme diphthongizes; vorbește does not)
How this differs from English and Spanish
As with Class I, English stems never move, so the instinct is to keep the infinitive vowel fixed and produce dorme, coborâ, iese uniformly. Spanish learners again have partial help: Spanish dormir diphthongizes too (duerme), and its distribution (singular and 3pl, absent in nosotros) rhymes with Romanian. But the diphthong is different — Spanish o→ue (duerme) versus Romanian o→oa (doarme) — and Romanian's plain Class IV keeps the 3pl as the bare stem (ei dorm), where Spanish diphthongizes (duermen). So the shape is similar but the details diverge; don't import Spanish forms wholesale.
Common Mistakes
❌ Copilul dorme liniștit.
Incorrect — the 3sg of a dormi diphthongizes: o → oa.
✅ Copilul doarme liniștit.
The child is sleeping peacefully.
❌ Trenul coborâ spre vale.
Incorrect — the 3sg diphthongizes: coboară.
✅ Trenul coboară spre vale.
The train descends toward the valley.
❌ Noi doarmim opt ore pe noapte.
Incorrect — in noi the ending is stressed, so the stem stays plain: dormim.
✅ Noi dormim opt ore pe noapte.
We sleep eight hours a night.
❌ El voarbește trei limbi.
Incorrect — -esc verbs never diphthongize; the stress is on the infix: vorbește.
✅ El vorbește trei limbi.
He speaks three languages.
❌ Ei doarme la bunici.
Incorrect — the 3pl of plain a dormi is the bare stem dorm, not the diphthong.
✅ Ei dorm la bunici.
They sleep at their grandparents'.
Key Takeaways
- Plain Class IV verbs diphthongize under 3rd-person stress, just like Class I: o→oa (doarme, coboară, moare), e→ie (iese), a→ă.
- The diphthong appears in the 3sg before -e (doarme); in plain -i verbs the 3pl is the bare stem (ei dorm), the reverse of Class I.
- The -î verbs (a coborî) keep the diphthong in the 3pl too (coboară).
- In noi/voi the ending takes the stress and the stem reverts to plain (dormim, coborâm).
- The -esc verbs never diphthongize: the stressed infix (vor-BESC) absorbs the stress, leaving the stem flat (vorbește, never voarbește).
- You must learn each -i verb's type (plain vs -esc) — a dormi and a vorbi look the same but behave oppositely.
Now practice Romanian
Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.
Start learning Romanian→Related Topics
- Class IV Present: -esc VerbsA2 — How to conjugate the dominant Class IV subtype that inserts -esc (or back-vowel -ăsc) in the singular and third-person plural — the single most common present-tense pattern in Romanian.
- Class IV Present: Plain -i VerbsA2 — How to conjugate the closed set of common Class IV (-i) verbs that take no -esc infix, including a dormi, a veni, and a simți, with their o → oa diphthongization.
- Stem Alternations: An OverviewB1 — The predictable vowel and consonant alternations that reshape Romanian verb stems across the paradigm — and why learning them once pays off across the whole grammar.
- Class I Present: Stem Vowel Changes (e→ea, o→oa, a→ă)A2 — The predictable stressed-stem diphthongizations that reshape Class I (-a) verbs in the third person — e→ea, o→oa, and the a→ă alternation — and why they appear exactly where the ending is unstressed.
- Class IV Present: -î VerbsB1 — How to conjugate the small but error-prone -î subtype of Class IV, where the î/â spelling rule and the optional -ăsc infix collide.