Subjunctive with Doubt and Denial

When the speaker expresses doubt, disbelief, denial, or uncertainty about something, the subjunctive is triggered. This is the "D" in the WEIRDO acronym. The reasoning is straightforward: if you doubt that something is true, you are not presenting it as a fact, so the indicative (the mood of facts) is inappropriate.

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The Core Principle

Certainty → Indicative	Doubt → Subjunctive
Creo que tiene razón.	No creo que tenga razón.
Es cierto que llueve.	No es cierto que llueva.
Sé que habla español.	Dudo que hable español.

Key rule: When the main clause expresses certainty or belief, use the indicative. When it expresses doubt, denial, or disbelief, use the subjunctive.

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Verbs and Expressions of Doubt

DUDAR QUE (to doubt that)

Dudar always triggers the subjunctive (when followed by que):