A complement clause (or noun clause) is a whole clause doing the job of a noun — usually the object of a verb like achar, saber, querer, or duvidar: Acho que vai chover ("I think it's going to rain"). The single most important thing to master here is the mood choice: whether the verb inside the complement is indicative or subjunctive is decided almost entirely by the matrix verb — the verb in the main clause. This page lays out that logic, covers complement clauses as subjects and as objects, the se indirect-question type, and the same-subject infinitive alternative.
Complement clauses as object and as subject
Most complement clauses are objects — they answer "what?" after the main verb.
Acho que vai chover hoje à tarde.
I think it's going to rain this afternoon. (Object of 'acho'.)
Ela disse que chega amanhã.
She said she's arriving tomorrow. (Object of 'disse'.)
Less commonly, a complement clause is the subject of the sentence — it answers "what is obvious / true / a shame?"
Que ele mentiu é óbvio.
That he lied is obvious. (Subject clause.)
É uma pena que você não possa vir.
It's a shame you can't come. (Extraposed subject clause — note the subjunctive 'possa'.)
In practice BR strongly prefers to extrapose a subject clause to the end — É óbvio que ele mentiu sounds far more natural than the front-loaded Que ele mentiu é óbvio, which is grammatical but formal/emphatic.
The mood choice is driven by the matrix verb
This is the heart of the page. The verb inside a complement clause is indicative or subjunctive depending on what kind of meaning the matrix verb expresses. The split is remarkably clean:
| Matrix verb expresses… | Mood in complement | Examples of matrix verbs |
|---|---|---|
| Assertion / belief / knowledge | Indicative | saber, achar, acreditar, ver, dizer, ter certeza |
| Desire / request / order | Subjunctive | querer, pedir, exigir, esperar, preferir |
| Doubt / denial | Subjunctive | duvidar, negar, não achar, não acreditar |
| Emotion / value judgment | Subjunctive | lamentar, temer, é bom que, é uma pena que |
Assertion and belief → indicative
When you assert something or report it as a fact you believe, the complement is indicative. You are presenting the content as real.
Eu sei que ele veio ontem.
I know he came yesterday. (Knowledge → indicative 'veio'.)
Acho que sim.
I think so. (Belief → indicative; 'que sim' is a fixed affirmative complement.)
The deep reason: the indicative is the mood of asserted reality. Saber and achar present their complement as something the speaker takes to be true, so it lives in the realm of fact — hence indicative.
Desire, doubt, emotion → subjunctive
When the matrix verb expresses a wish, a doubt, or an emotional reaction, the complement is subjunctive. The content is not being asserted as fact — it is wanted, doubted, or merely reacted to.
Quero que você venha mais cedo.
I want you to come earlier. (Desire → subjunctive 'venha'.)
Duvido que ele venha.
I doubt he'll come. (Doubt → subjunctive 'venha'.)
Lamento que ela não esteja aqui.
I'm sorry she isn't here. (Emotion → subjunctive 'esteja'.)
The logic is consistent: the subjunctive marks content that exists in the realm of wishes, doubts, and possibilities rather than asserted reality. Querer que describes something you want to become true (not yet a fact); duvidar que explicitly withholds the assertion; lamentar que reacts to something without the point being to assert it.
The negation flip
Negating a belief verb often pushes its complement into the subjunctive, because negating "I think X" turns it into "I don't assert X" — doubt territory.
Acho que ele está em casa.
I think he's home. (Asserted belief → indicative.)
Não acho que ele esteja em casa.
I don't think he's home. (Negated belief → doubt → subjunctive.)
Same-subject contexts → bare infinitive
When the matrix verb and the complement would share the same subject, BR drops the que-clause entirely and uses a bare infinitive. You do not say quero que eu vá; you say quero ir.
Quero sair agora.
I want to leave now. (Same subject → infinitive, no 'que', no subjunctive.)
Quero que você saia agora.
I want you to leave now. (Different subjects → finite subjunctive.)
Ela espera passar no vestibular.
She hopes to pass the entrance exam. (Same subject → infinitive.)
This mirrors English closely (I want to leave vs. I want you to leave), so the contrast is intuitive. The only thing to internalize is that BR will never use a finite same-subject que-clause where the infinitive is available.
Interrogative complements with se
When the complement is an indirect question ("whether / if something is the case"), it is introduced by se instead of que. These are common after verbs of knowing, asking, and wondering, and they take the indicative.
Não sei se ela vem.
I don't know whether she's coming.
Me pergunto se valeu a pena.
I wonder whether it was worth it.
Ele perguntou se eu tinha terminado.
He asked whether I had finished.
Note that this se means "whether/if" as an indirect-question marker — it is not the conditional se ("if you study, you'll pass"). The complement is a yes/no question turned into a noun clause.
Que-deletion is rare in BR
English freely drops "that" — I think he's coming. BR is much more conservative: the complementizer que is normally retained. Dropping it (Acho ele vem) sounds wrong in standard BR and appears only in very casual speech with a handful of verbs.
Acho que ele vem.
I think he's coming. (Standard BR keeps 'que'.)
Common Mistakes
❌ Acho ele vem amanhã.
Incorrect — BR doesn't drop the complementizer 'que' the way English drops 'that'.
✅ Acho que ele vem amanhã.
I think he's coming tomorrow. (Keep 'que'.)
❌ Quero que eu vá à festa.
Incorrect — same subject can't take a finite 'que'-clause; use the infinitive.
✅ Quero ir à festa.
I want to go to the party. (Same subject → infinitive.)
❌ Quero que você vem mais cedo.
Incorrect — 'querer que' triggers the subjunctive, so it must be 'venha', not the indicative 'vem'.
✅ Quero que você venha mais cedo.
I want you to come earlier. (Subjunctive after a verb of desire.)
❌ Não acho que ele está em casa.
Incorrect — negating the belief verb introduces doubt, which requires the subjunctive.
✅ Não acho que ele esteja em casa.
I don't think he's home. (Negated belief → subjunctive.)
❌ Não sei que ela vem.
Incorrect — an indirect yes/no question uses 'se' (whether), not 'que'.
✅ Não sei se ela vem.
I don't know whether she's coming. (Interrogative complement with 'se'.)
Key Takeaways
- A complement clause is a que- or se-clause functioning as the subject or object of the main verb.
- Mood is decided by the matrix verb: assertion/belief/knowledge → indicative; desire/doubt/emotion → subjunctive.
- Negating a belief verb flips the complement to subjunctive (doubt): acho que vem → não acho que venha.
- Same subject → bare infinitive (quero sair), never a finite same-subject que-clause.
- Indirect yes/no questions use se ("whether"); BR keeps que where English would drop "that."
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Start learning Portuguese→Related Topics
- Subordination: OverviewB1 — The three types of subordinate clause in Brazilian Portuguese — noun, relative, and adverbial — plus finite vs. non-finite subordination and BR's unique personal infinitive.
- Subjunctive after Verbs of Desire and WillA2 — Why querer que, pedir que, and other verbs of wanting force the subjunctive — and the English-speaker error to avoid.
- Adverbial ClausesB1 — How Brazilian Portuguese builds time, cause, condition, concession, purpose, result and comparison clauses — and why each conjunction picks the indicative or the subjunctive.
- Relative Clause SyntaxB1 — The structure of Brazilian Portuguese relative clauses — que, quem, o qual, cujo, onde — and the major split between standard pied-piping and the spoken-BR resumptive/dropping strategies.
- Conjunctions and Mood SelectionB1 — The master table mapping each Brazilian Portuguese conjunction to the mood it governs — indicative, subjunctive, or future subjunctive — and the assertion principle that predicts them all.