The expression "dudo que" (I doubt that) takes the subjunctive mood because it expresses doubt, uncertainty, or disbelief regarding the action or state of the clause that follows. The subjunctive mood is used in Spanish to convey scenarios that are not certain or objective, which aligns with the meaning of "dudo que."
For example:
- Dudo que él venga. (I doubt that he is coming.) – Here, the speaker expresses uncertainty about whether he will come, so the subjunctive "venga" is used.
On the other hand, "no dudo que" (I do not doubt that) conveys certainty or assurance about the action or state that follows. In this case, it indicates that the speaker believes the statement to be true and, therefore, the indicative mood is used.
For example:
- No dudo que él viene. (I do not doubt that he is coming.) – The speaker is expressing confidence or belief about the action, thus using the indicative "viene."
In summary, the key difference lies in the level of certainty: "dudo que" implies uncertainty and requires the subjunctive, while "no dudo que" implies certainty and requires the indicative.