Certainty and doubt: indicative versus subjunctive

In brief

In Brazilian Portuguese, the speaker’s attitude toward a statement can change the verb mood. Use the indicative to present something as a fact or a belief you accept; use the subjunctive when the main clause casts doubt on it or presents it as a possibility. English often uses the same verb form in both cases.

Form

Compare acho que + indicative with não acho que, duvido que, or é possível que + subjunctive in the following clause. The mood change appears on the verb after que.

Usage

• Use the indicative after an affirmative expression of belief, such as acho que.
• Use the subjunctive after expressions of doubt or uncertainty, such as não acho que, duvido que, and é possível que.
• Negating a belief can change the mood: acho que ela está … but não acho que ela esteja … .

Examples

• Acho que ela está em casa. — I think she’s at home.
• Não acho que ela esteja em casa. — I don’t think she’s at home.
• Duvido que eles tenham tempo. — I doubt they have time.
• É possível que chova amanhã. — It might rain tomorrow.

Common mistake

❌ Não acho que ela está em casa.

✅ Não acho que ela esteja em casa.

After não acho que, standard Brazilian Portuguese uses the subjunctive (esteja) to express the speaker’s doubt, even though English keeps the same form in ‘I think’ and ‘I don’t think’.

Remember

Ask whether the main clause presents the statement as a belief or questions it. That choice guides the mood after que.