Devi: Must Or Ought

Devi is the regular verb used when circumstances, rules, or reasoning make an action necessary: “must,” “have to,” “be supposed to,” or “ought to.” It most often takes an infinitive whose understood subject is the same as the subject of devi. The same verb can also express a strong conclusion—English “must” in “She must be home”—so context decides whether the necessity is practical or inferential.

The complete paradigm

Nothing in devi is irregular. The stem dev- combines with the six ordinary verb endings, and the finite forms never change for person or number.

The tense ending locates the necessity, not necessarily the action. Mi devis telefoni al ŝi says that an obligation to call existed; it does not say whether the call happened. English often leaves that distinction unclear too, but Esperanto lets you state the result separately.

The volitive devu is grammatically regular but uncommon in ordinary instructions. A rule normally states Vi devas porti insignon, not Vi devu porti insignon. Devu belongs mainly in an expressed wish or demand about the obligation itself, a comparatively specialized use.

Necessity and the infinitive complement

The central frame is subject + devi + infinitive. The subject of devi is also the understood subject of the infinitive. Any object belongs to the infinitive and therefore keeps its accusative -n.

Here pro la ŝtormo gives the reason for the necessity. It is not a complement selected by devi. Esperanto usually leaves the source implicit when it is obvious from a law, schedule, promise, physical circumstance, or the speaker’s judgment.

Unlike English owe, devi in this use does not take the thing required as a direct object. Say Mi devas pagi la kotizon, not Mi devas la kotizon. The infinitive names the required action.

When another person is to perform the necessary action, everyday Esperanto generally makes that person the subject of devi: Vi devas veni. An impersonal alternative is Necesas, ke vi venu, where the desired or necessary action appears in a ke-clause with -u.

Obligation, expectation, and inference

With a controllable action, devi usually presents an obligation or practical necessity. With schedules and arrangements it can mean “be due/supposed to.”

With a state or conclusion, devi often marks strong inference: the available evidence makes the statement highly likely. This is not a command addressed to the subject.

In the last example, devis places the inferred state in the past. The surrounding evidence, not a special verb form, tells us that the meaning is inferential. The dedicated epistemic modality page develops this contrast.

Why devus often means “should”

Devus presents necessity under a condition, as an unrealized expectation, or at a respectful distance. That makes it the normal equivalent of advisory English “should” and “ought to.” The force ranges from gentle advice to criticism depending on context and tone.

The compound devus esti alveninta combines conditional necessity with a completed active participle: according to the expectation, the arrival would already be complete. Such compounds are precise but heavier than simple forms. Use them when the time relation matters, not merely to imitate an English perfect.

Negation: two meanings that English blurs

Logically, the position of ne determines its scope:

• ne devi fari: there is no obligation to do it;
• devi ne fari: there is an obligation not to do it.

Traditional and modern usage also attests ne devas with the meaning “must not,” following the surface pattern of several national languages. It is accepted usage, but it can conflict with the logical “not obliged” reading. The clearest pedagogical choice is devas ne for prohibition and ne bezonas or ne estas necese for lack of obligation. This is one place where actual usage is less tidy than the underlying scope rule.

Participles and the productive family

The infinitive after modal devi can be analyzed as its object or verbal complement, but devi normally has no ordinary noun patient that could become the subject of a passive. Its active participles are therefore much more natural than passive ones: devanta “currently obliged,” devinta “formerly/having been obliged,” and devonta “about to be obliged.” Finite compounds such as estas devinta are possible but often stiff; a simple devis is usually better. Esperanto does not normally passivize the infinitival complement, so forms such as devata should not be manufactured merely because the endings exist.

The root has a useful, productive family:

Notice the valency change: devi fari has the obligated person as subject, while devigi iun fari adds a causer as subject and marks the compelled person with -n. This is a systematic effect of -ig-, not an irregularity of devi.

Frequency and register

Devi, devas, devis, devos, and devus are neutral and extremely frequent in speech and writing. Deviga, devo, and devigi are also standard in everyday and institutional contexts. Devu and elaborate participial compounds are grammatical but less frequent; in ordinary conversation speakers favor a direct finite form or a clearer paraphrase. No special formal conjugation exists.

Common Mistakes

Putting a finite verb after devi

Copying English “must” as an invariable word

Giving modal devi a noun object

Treating devus as a past tense

Adding an English-style auxiliary

Key Takeaways

Use devi + infinitive when the same subject is under an obligation, necessity, or strong expectation. Choose devis and devos according to the time of that necessity, and devus for conditional necessity or advice. For transparent negation, separate “must not” (devas ne) from “does not have to” (ne bezonas). The family devo—deviga—devigi shows how the regular root and Esperanto’s derivational system work together.