In a sentence, the grammatical mood conveys the speaker’s attitude about the state of being of what the sentence describes. This may sound a little complicated, but it’s simple enough: In the indicative mood, for instance, the speaker is sure that something is the case, while in the imperative mood the speaker desires that something should happen.
Mood is only one of many verb properties, others being tense, aspect, and voice. It is expressed through the sentence’s verbs and grammatical structure. For example, a sentence that lacks a subject and begins with a present-tense verb is likely imperative, and a sentence that begins with if and uses past-tense verbs is likely subjunctive.
Linguists have defined dozens of moods used in languages throughout the world, but English only uses three.
The indicative mood is used to make factual statements, ask questions, or express opinions as if they were facts. Any verb tense may be deployed in the indicative mood.
The following sentences are statements of fact or belief, so they are in the indicative mood:
I saw something today that really annoyed me. [Vitrearum's Church Art]
He lives most of the year in Spain but returns regularly to visit his ailing mother. [Sydney Morning Herald]
Vikings will be the new vampires. [Nile Guide]
Prosecutors have not said whether they will appeal the decision. [New York Times]
A sentence in the imperative mood expresses commands or requests. It indicates that the speaker desires for the action expressed in the sentence to take place. In most imperative sentences, there’s an implied you. These sentences are in the imperative mood:
Sit on the sofa.
Let me go to bed
The subjunctive mood is complicated. For an in-depth explanation, see our post on the subject.