Modalnost - trebati, valjati, morati i potencijal
Overview
Морати is already known as a fully personal necessity verb (from the A1 lesson on basic conjunctions; the да-clause machinery in the B1 lesson on complex sentences was built partly on it). This lesson takes требати further than the impersonal треба да of the A2 lesson on modal verbs and adds ваљати - both impersonal whenever they govern an action (требати's needing-a-thing pattern, below, is the one that agrees), both near-synonyms of necessity or propriety, but pulling apart sharply in strength and register - and shows how the би from the B1 lesson on conditionals softens all three into the hedged, polite register a C1 speaker needs day to day.
The lesson on да-constructions vs. the infinitive already mapped the да-versus-infinitive mechanism that требати's own verbal complement runs on; this lesson assumes that and focuses on what's new here: the three verbs' necessity semantics against each other, морати's second, epistemic life, and the би-softened potential forms built on all three.
Требати - the everyday, neutral necessity verb
In its да-clause/infinitive pattern for necessity to act, требати is impersonal in the Serbian standard - it stays a frozen 3rd-singular form no matter who needs to act, exactly like нема (as the B1 lesson on the genitive of negation covers). Personal forms (требам да, требају да) are colloquial in Serbian, and standard in Croatian. Its verbal complement follows the subject-based split from the lesson on да-constructions vs. the infinitive: a bare infinitive for a fully generic statement (Треба много вежбати. - "One must practice a lot"), да + present agreeing with a specific subject the instant one is named (Треба да вежбаш више. - "You need to practice more").
Требати also has a second, unrelated pattern, for needing a thing rather than needing to do something: a dative experiencer plus a nominative theme, Треба ми одмор. (I need rest). This looks superficially like the нема/немати family from the B1 lesson on the genitive of negation, but it isn't one - negated, требати still keeps the theme in its base form: Не треба ми твоја помоћ овог пута. (I don't need your help this time), never a genitive *помоћи. The B1 lesson on the genitive of negation already limited its own rule to (не)мати/(не)бити specifically; требати simply falls outside that rule, despite the surface resemblance to нема. Unlike the да-clause pattern, this one is not frozen: the nominative theme is требати's real grammatical subject here, so the verb agrees with it in person and number, exactly like any ordinary verb - singular Треба ми одмор. against plural Требају ми паре. (I need money), and just as readily 2nd person when the thing needed is a person rather than an object: Требаш ми. (I need you - literally "you are needed to me").
Ваљати - the literary, proverbial register
The impersonal ваља (from ваљати, to be worth/be fitting) shares требати's basic shape - frozen, impersonal, generally a bare infinitive complement - but sits in a noticeably more literary, formal or proverbial register: Ваља поштовати старије. ("One ought to respect one's elders") reads like a maxim, where Треба поштовати старије. reads like ordinary advice. Ваља does take a да-clause - the softened ваљало би да below is one - but far less often than требати; its home is the generic, infinitive-complement lane.
Negated, не ваља idiomatically broadens well past strict necessity into a general negative evaluation - it's not good, that's improper - not just one shouldn't: Не ваља тако одговарати старијима. can mean either you shouldn't answer your elders like that or, just as often, simply that's not a proper way to answer your elders, with no distinct necessity reading intended at all.
Морати - the strongest necessity, and its epistemic second life
Of the three, морати is the strongest and the only fully personal one - морам, мораш, мора, and so on through every person, the verb the A1 lesson on basic conjunctions already glossed as must - closest to English must/have to. It is also the one that reads epistemically at full strength, as a confident inference from evidence rather than an obligation. Мора да ради цео дан - телефон му је искључен. (He must be working all day - his phone is off.) states a conclusion, not a duty; compare the deontic Мора да заврши извештај до петка. (He has to finish the report by Friday), a genuine obligation. The surface shape is identical - мора да + present - and only context or surrounding evidence tells the two apart.
Требати and ваљати live mostly in the deontic, advisability lane, but требати has a weaker epistemic use of its own - an expectation rather than a conclusion: Требало би да је већ код куће. (He should be home by now), Треба да стигну сваког часа. (They should arrive any minute). In careful academic prose this is the usual way to hedge a claim. Ваљати's old epistemic ваља да survives mostly fossilized in the adverb ваљда (probably, I suppose). That strong inferential reach - „it must be the case that…“ - is морати's alone among the three.
Softening all three with the potential
The би + participle from the B1 lesson on conditionals softens any of the three into a hedged, polite suggestion rather than a flat directive: требало би да, ваљало би да, морао би да. In their да-/infinitive pattern требати and ваљати are impersonal, so their participle agrees with nothing there - it stays frozen neuter singular, требало/ваљало, regardless of who is being advised: Требало би да позовеш лекара. ("You should call a doctor"), said to a man or a woman alike. Требати's needing-a-thing pattern is the exception, exactly as in the present: its nominative theme is a real subject, so the participle agrees with it - Требала би ми помоћ. (I could use some help), Требао би ми одмор, Требале би ми паре. Морати, being genuinely personal, keeps the ordinary participle agreement from the B1 lesson on conditionals: Морао би озбиљније да схвати ситуацију. for a man, Морала би озбиљније да схвати ситуацију. for a woman ("he/she should take the situation more seriously").
This divergence is not an extra rule to memorize - it falls straight out of what each pattern already is: where a verb is impersonal it has no real subject for a participle to agree with, so its би-form stays invariant; where it has one - морати always, требати with the thing needed - the participle agrees exactly as the B1 lesson on conditionals already established for every other verb. In everyday speech you will also hear personal forms in the да-pattern - Требао бих да кренем, Требала би да дође. - common enough that usage handbooks call them hard to avoid; careful writing, and the standard this course teaches, keeps the invariant Требало би да кренем.
Tables
| Verb | Strength / register | Person agreement | Example |
|---|---|---|---|
| trebati | neutral, everyday | none - impersonal treba (verbal complement); agrees with the subject in the trebati mi pattern | Treba da se odmoriš. |
| valjati | bookish, proverbial, prescriptive | none - impersonal valja | Valja poštovati starije. |
| morati | strong, binding | fully personal: moram, moraš… | Mora da završi izveštaj. |
Examples
Compared with…
English must is one of the closer transfers in the whole course specifically for морати: it carries both the deontic (You must finish this) and the epistemic (He must be home) reading, disambiguated by context exactly the same way as мора да. Should maps loosely onto требало би, though English collapses the impersonal/personal distinction this lesson draws between требало би and морао би into one invariant word. Требати and ваљати have only a weak epistemic use - Требало би да је већ код куће. matches English He should be home by now well - but on the deontic side they don't map as neatly: English should covers ground that Serbian splits across two different, register-marked verbs.
Common mistakes
Tips & exceptions
- In its да-/infinitive pattern требати is impersonal in the Serbian standard - треба for every person; the personal требам да is colloquial (and standard in Croatian), so do not default to it. The needing-a-thing pattern, with its dative experiencer, is the one that agrees (next tip).
- Требати is frozen impersonal only in its да-clause/infinitive pattern (Треба да…/Треба + infinitive). In its other pattern, needing a thing, the nominative theme is the real subject and требати agrees with it in person and number: „Треба ми одмор.“ but „Требају ми паре.“ - don't over-apply the always impersonal rule to this second pattern.
- To soften a directive or make it more polite, drop a би onto the modal (требало би, морао би) - the exact same потенцијал mechanism the B1 lesson on conditionals taught for би + participle, just applied to a modal verb.
- Морати carries the strong epistemic „must be…“ reading; требати has only a weaker, expectation-type one (Требало би да је већ код куће.), and ваљати's survives mainly in ваљда.
- The personal требам да agreement pattern is standard in Croatian and colloquial in Serbian - recognize it, but in the standard this course teaches use треба да.
- Не ваља idiomatically broadens to mean that's not good/that's improper well beyond strict necessity - worth learning as its own fixed expression rather than composing it fresh each time.
- Мора да's epistemic reading needs context to disambiguate from the deontic one - a genuinely ambiguous sentence out of context („Мора да ради.“) could mean either he has to work or he must be working; intonation resolves it in speech, surrounding sentences in writing.