sumnjati (to doubt / suspect) | Croatian Grammar

Sumnjati is the Croatian verb for both doubting and suspecting — English keeps these apart with two words, Croatian folds them into one and lets the construction disambiguate. The headline fact is its government: sumnjati takes u + accusative ("doubt / suspect something or someone") — sumnjati u nekoga ("suspect someone"), sumnjati u sebe ("doubt oneself") — and a da-clause ("doubt that…"). Get that preposition right and the rest follows. Sumnjati is the natural counterweight to vjerovati ("to believe"): where vjerovati trusts, sumnjati withholds trust.

Aspect

Sumnjati is imperfective — doubting and suspecting are mental states, and states default to the imperfective. There is a prefixed perfective posumnjati ("to begin to suspect, grow suspicious"), which marks the onset of suspicion rather than the standing state. You will use sumnjati for "I doubt / I suspect (now)" and posumnjati for the moment doubt sets in.

Verb	Aspect	Present 1sg	Typical use
sumnjati	imperfective	sumnjam	the ongoing state: doubt / suspect (default)
posumnjati	perfective	posumnjam	"begin to suspect" — the onset of doubt

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One preposition does almost all the work: sumnjati u + accusative. Sumnjam u njega = "I suspect/doubt him". Sumnjam u to = "I doubt that". Don't reach for a bare accusative or for "na" — it is always u + accusative, or a da-clause.

Present tense

A regular a-class verb: stem sumnja- + -m, -š, -∅, -mo, -te, -ju.

Person	Form
ja	sumnjam
ti	sumnjaš
on/ona/ono	sumnja
mi	sumnjamo
vi	sumnjate
oni/one/ona	sumnjaju

Sumnjam u njegovu priču, previše je glatka.

I doubt his story, it's too smooth. — 'u + accusative' government ('u njegovu priču').

Policija sumnja u susjeda, ali nema dokaza.

The police suspect the neighbour, but they have no proof. — 'suspect' reading, 'u + accusative'.

The l-participle

Regular for the -ati infinitive: masculine sumnjao, feminine sumnjala.

Gender / number	Form
masculine singular	sumnjao
feminine singular	sumnjala
neuter singular	sumnjalo
masculine plural	sumnjali
feminine plural	sumnjale
neuter plural	sumnjala

Perfect tense (perfekt)

Clitic biti + l-participle. With the imperfective sumnjati the perfekt reads "doubted / suspected (over a stretch of time)".

Person	Masculine subject	Feminine subject
ja	sumnjao sam	sumnjala sam
ti	sumnjao si	sumnjala si
on / ona	sumnjao je	sumnjala je
mi	sumnjali smo	sumnjale smo
vi	sumnjali ste	sumnjale ste
oni / one	sumnjali su	sumnjale su

Oduvijek sam sumnjao u te brze zarade.

I've always been suspicious of those quick profits. — masculine 'sumnjao', 'u + accusative'.

Future I (futur prvi)

The infinitive drops its -i: sumnjat ću, never sumnjati ću.

Person	Form
ja	sumnjat ću
ti	sumnjat ćeš
on/ona/ono	sumnjat će
mi	sumnjat ćemo
vi	sumnjat ćete
oni/one/ona	sumnjat će

Ako opet zakasni, svi će sumnjati u njegove izgovore.

If he's late again, everyone will doubt his excuses. — future 'sumnjat će' + 'u + accusative'.

Imperative

The imperative sumnjaj! / sumnjajte! exists but is uncommon — you rarely command someone to doubt. You will more often meet the negative Ne sumnjaj ("Don't doubt [it]") as reassurance.

Person	Form
ti	sumnjaj
mi	sumnjajmo
vi	sumnjajte

Ne sumnjaj u sebe, dobro si to napravila.

Don't doubt yourself, you did it well. — negative imperative + reflexive 'u sebe'.

Conditional I (kondicional prvi)

The bih-clitics + l-participle, for hypotheticals.

Person	Form (masc.)
ja	sumnjao bih
ti	sumnjao bi
on/ona/ono	sumnjao/sumnjala/sumnjalo bi
mi	sumnjali bismo
vi	sumnjali biste
oni/one/ona	sumnjali bi

Da nije bilo onog poziva, ne bih ni u koga sumnjao.

If it hadn't been for that call, I wouldn't have suspected anyone. — conditional + negative 'ni u koga'.

Other forms

Passive participle: none in normal use — sumnjati is intransitive (its complement is a prepositional phrase, not an accusative object, so there is nothing to passivise). The related adjective is sumnjiv ("suspicious, suspect"), and the noun is sumnja ("doubt, suspicion").
Verbal adverb (impf): sumnjajući ("[while] doubting") — possible but rare.

Cijela priča mi je sumnjiva od početka.

The whole story has seemed suspicious to me from the start. — the related adjective 'sumnjiv'.

Key uses and government

1. u + accusative — "doubt / suspect (something or someone)"

This is the central pattern. The thing or person doubted/suspected takes u + accusative. With a person it reads "suspect"; with a thing or proposition it reads "doubt". See the accusative for the case itself, and verb government for prepositional rection.

Ne sumnjam u tvoje namjere, samo me brine plan.

I don't doubt your intentions, the plan just worries me. — 'u + accusative' ('u tvoje namjere').

Sumnjam u sebe svaki put prije ispita.

I doubt myself every time before an exam. — reflexive 'u sebe', 'doubt oneself'.

2. da-clause — "doubt that…"

With a full proposition, sumnjati takes a da-clause. Important nuance: sumnjati da leans toward "doubt that" (expecting the thing won't happen) — so Sumnjam da će doći means "I doubt he'll come", not "I suspect he'll come". To say "I suspect that something is so", Croatian more often uses sumnjam da in the literary/older "suspect" sense or rephrases with čini mi se da ("it seems to me that"). For the clause-vs-infinitive choice generally, see da vs the infinitive.

Sumnjam da će stići na vrijeme po ovom prometu.

I doubt he'll make it on time in this traffic. — 'sumnjati da' = 'doubt that'.

Sumnjam da je to istina.

I doubt that's true. — the negative-expectation reading of 'sumnjati da'.

3. The counterweight: vjerovati — "to believe"

Sumnjati is the natural opposite of vjerovati ("to believe / trust"). Note the contrast in their government, which trips learners up: vjerovati takes the dative of a person you trust (vjerujem ti — "I believe you"), whereas sumnjati takes u + accusative of a person you suspect (sumnjam u tebe — "I suspect you"). Same semantic axis, opposite case frames.

Vjerujem ti, ali sumnjam u njega.

I believe you, but I'm suspicious of him. — 'vjerovati' + dative vs 'sumnjati u' + accusative, side by side.

4. posumnjati — the onset of suspicion

The perfective posumnjati marks the moment doubt or suspicion kicks in: "to grow suspicious, to start to suspect". Same u + accusative government.

Posumnjao sam u nju tek kad je promijenila priču.

I only grew suspicious of her when she changed her story. — perfective onset 'posumnjao', 'u + accusative'.

Common Mistakes

❌ Sumnjam njega.

Missing the preposition — 'sumnjati' governs 'u + accusative': 'Sumnjam u njega'.

✅ Sumnjam u njega.

I suspect him.

❌ Sumnjam na tvoje namjere.

Wrong preposition — it's 'u', not 'na': 'sumnjam u tvoje namjere'.

✅ Sumnjam u tvoje namjere.

I doubt your intentions.

❌ Sumnjam u to da će doći.

Overbuilt — with a 'da'-clause you don't also need 'u to': just 'Sumnjam da će doći'.

✅ Sumnjam da će doći.

I doubt he'll come.

❌ Sumnjam ti.

That's the frame for 'vjerovati' (believe) — 'sumnjati' takes 'u + accusative', not the dative: 'sumnjam u tebe'.

✅ Sumnjam u tebe.

I'm suspicious of you / I doubt you.

❌ Sumnjati ću u njegovu verziju.

Future spelling — the infinitive drops its -i before the clitic: 'sumnjat ću'.

✅ Sumnjat ću u njegovu verziju.

I'll be suspicious of his version.

Key Takeaways

Sumnjati (impf, present sumnjam) covers both "doubt" and "suspect"; perfective posumnjati = "begin to suspect".
Core government: u + accusative — sumnjati u nekoga ("suspect someone"), sumnjati u sebe ("doubt oneself").
With a clause, sumnjati da leans "doubt that" (negative expectation): Sumnjam da će doći = "I doubt he'll come".
It is the counterweight to vjerovati — but note the frames differ: vjerovati
- dative (vjerujem ti) vs sumnjati u
  - accusative (sumnjam u tebe).
Intransitive (no passive participle); related forms: adjective sumnjiv, noun sumnja. Future: sumnjat ću, never sumnjati ću.

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