The verb a fi has both fi and fii, but they belong to different constructions. Compare Fii atent! (Be careful!) with Nu fi atent la zgomot! (Do not pay attention to the noise!) and Vreau să fii atent. (I want you to be careful.)
What is the basic difference between fi and fii?
Write fii for the affirmative tu imperative and for the present subjunctive with a second-person singular subject. Write fi for the infinitive, the negative tu imperative, and several compound forms.
| Construction | Target spelling | Natural example | What the form is doing |
|---|---|---|---|
| Affirmative imperative, tu | fii | Fii calm! (Stay calm!) | A direct positive command to one familiar person |
| Present subjunctive, tu | fii | Sper să fii bine. (I hope you are well.) | A să clause whose subject is tu |
| Negative imperative, tu | fi | Nu fi trist! (Do not be sad!) | nu plus the infinitive without a |
| Infinitive | fi | A fi sincer este important. (Being honest is important.) | The dictionary or independent infinitive |
| Compound form | fi | Voi fi acolo. (I will be there.) | A bare infinitive used with an auxiliary |
When do you write fii?
There are two central uses of fii: the affirmative singular imperative and the second-person singular present subjunctive. In both cases, the form refers to one familiar addressee, but the surrounding construction tells you which use it is.
- Use the affirmative imperative for a direct command: Fii atent! (Be careful!), Fii realist! (Be realistic!), Fii aici la opt! (Be here at eight!).
- When the second verb after să has a tu subject, use the present subjunctive: Vreau să fii atent. (I want you to be careful.); E bine să fii punctual. (It is good for you to be punctual.)
- Use the same spelling in the future frame o să before a second-person singular form: O să fii acasă la prânz. (You will be at home at lunchtime.) Here o să marks the future, rather than a wish or command.
When do you write fi?
Write fi when the form is the infinitive or when an auxiliary construction uses the bare infinitive. The negative singular imperative also uses this one-i form, even though its meaning is addressed to tu.
| Context | Correct pattern | Natural example | Diagnostic |
|---|---|---|---|
| Dictionary or independent infinitive | a fi | A fi politicos contează. (Being polite matters.) | The particle a introduces the infinitive |
| Negative infinitive | a nu fi | A nu fi pregătit nu înseamnă că ai pierdut. (Not being ready does not mean that you have lost.) | nu comes inside the infinitive phrase after a |
| Negative imperative, tu | nu fi | Nu fi supărat! (Do not be upset!) | nu + the infinitive without a |
| Future or conditional auxiliary | voi fi, aș fi, ar fi | Aș fi mai calm în locul tău. (I would be calmer in your place.) | An auxiliary is followed by bare fi |
| Past subjunctive or another compound form | să fi, să fi fost | Să fi fost acolo, te-aș fi ajutat. (If I had been there, I would have helped you.) | fi is followed by a participle or belongs to a compound form |
Do not decide from nu alone: identify the whole construction. Nu fi obosit! is a negative command to tu, while a nu fi obosit is a negative infinitive. The words before and after the form show whether you are reading a command or an infinitive phrase.
How is fii different from ești and fiți?
Fii is not the ordinary present-tense form of a fi. The present indicative uses ești for tu, while fiți is the second-person plural or formal form in the imperative and subjunctive. The surrounding words identify the construction. Ești atent? (Are you careful?) is a present-tense question. Fii atent! (Be careful!) is a command. Vreau să fii atent. (I want you to be careful.) is a să clause.
| Person or use | Present indicative | Affirmative imperative | Present subjunctive |
|---|---|---|---|
| tu | ești | fii! | să fii |
| voi | sunteți | fiți! | să fiți |
| dumneavoastră | sunteți | fiți! | să fiți |
Mistakes to avoid
- Do not write Nu fii! for the ordinary singular negative command. The affirmative is Fii calm!, but the negative is Nu fi calm! (Do not be calm!), with one i.
- Do not use fii after the infinitive marker: write a fi, not a fii.
- Do not use fii after voi, aș, or ar: write voi fi, aș fi, and ar fi.
- Do not replace the present indicative ești with fii: Tu ești obosit. (You are tired.) describes a state; Fii odihnit! (Be well-rested!) gives an instruction.
- Do not reduce the rule to “two i after să.” The second-person present subjunctive is să fii, but the past subjunctive has să fi fost and therefore one i in fi before the participle.
You are telling one familiar person to be careful. Which sentence is correct?
- Fi atent!
- Fii atent!
- Fiiți atent!
- Să fi atent!
The affirmative singular imperative of a fi is Fii!. Use fi in infinitive and negative-imperative contexts. Fiți is plural or formal. The subjunctive option needs the second i: să fii.
Complete the sentence: Vreau să ___ sincer cu mine.
- fi
- fie
- fiți
- fii
The understood subject of să fii is tu, so the second-person singular present subjunctive is fii. Fi is the one-i form used in other constructions. Fie is third person. Fiți is plural or formal.
Which sentence uses the infinitive form of a fi?
- Fii liniștit!
- Nu fi liniștit!
- A fi liniștit ajută.
- Să fii liniștit!
A fi liniștit is an infinitive phrase introduced by a, so it uses fi. The other options are an affirmative imperative, a negative imperative, and a subjunctive construction.
Which sentence gives a negative command to one familiar person?
- Nu fii grăbit!
- Nu ești grăbit!
- Nu fi grăbit!
- Nu fiți grăbit!
The singular negative imperative is nu plus the infinitive without a: Nu fi grăbit!. Nu ești grăbit is a present-tense statement. Nu fii copies the affirmative imperative spelling, which the singular negative imperative does not use. Fiți is plural or formal.
Which sentence uses fi in a compound form rather than fii in a command or second-person subjunctive?
- O să fii acasă.
- Fii atent!
- Sper să fii bine.
- Voi fi acasă mâine.
In voi fi, fi is the bare infinitive after the future auxiliary voi. The other sentences use fii after o să, in the affirmative imperative, or after să with a tu subject.