Mood is the use of form to indicate semantic and grammatical differences in the manner of the action of a verb. Three moods are used in English.
Indicative mood is used to state a fact or ask a question:
Imperative mood is used to issue a command or make a request:
Subjunctive mood is used to express doubt, wishing, belief, or improbability:
The subjunctive mood is indicated through a shift in tense when the dependent clause follows a wish statement, or is an improbable if clause.
Probable if clause:
Sentences that express urging, demand, or necessity also require the subjunctive mood. Verbs other than the verb 'to be' in the dependent clause use the present tense form of the verb, without adding the 's' for the third person singular:
Such sentences that require the verb 'to be' in the dependent clause use the form 'be' in all three persons: