When should I use the present subjunctive?

The subjunctive is a mood expressing the uncertainty or doubt of a speaker. To express this uncertainty, the speaker switches from the indicative (hablo/hablas/habla/hablamos/hablais/hablan) to the subjunctive mood (hable/hables/hable/hablemos/hableis/hablan).Julia habla el chino. This sentence is in the indicative because it is a known fact.Es probable que Julia hable el chino. This sentence is in the subjunctive mood because whether she speaks Chinese or not is unknown.Phrases such as 'es probable que', 'es posible que' and 'es importante que' are subjunctive triggers as they express uncertainty or doubt. Hope and desire are also subjunctive triggers, shown in the example below:Julia escucha música rock. (Indicative).Dudo que Julia escuche música rock. (Subjunctive).The second sentence expresses doubt whereas the first sentence states a fact.Therefore, we should use the subjunctive when:1) we want to express doubt or uncertainty ('dudo que')2) we see the phrase 'es probable que', 'es posible que', or 'es importante que' (the verb which follows will be in the subjunctive mood)3) we want to express a hope or desire ('espero que')