Mood is that property of verbs which shows the manner in which the action or state is expressed.
Mood (or mode) is derived from the Latin word modus, manner.
Compare the following sentences, noting the form of the verb in each.
1. Richard is quiet.
2. Is Richard quiet?
3. If Richard were quiet, I might study.
4. Richard, be quiet.
In the first and second sentences, the form IS is used to assert or question a fact. In the third, the form WERE expresses a condition or supposition that is contrary to fact. In the fourth, the form BE expresses a command or request.
The difference in form seen in the verb in these sentences is called a difference of mood.
There are three moods - the indicative mood, the imperative mood and the subjunctive mood.
1. The indicative mood is the mood of simple assertion or interrogation, but it is used in other constructions also.
2. The imperative mood is the mood of command or request.
3. The subjunctive mood is used in certain special constructions of wish, condition and the like.
Thus, in the above examples, IS is in the indicative, WERE in the subjunctive and BE in the imperative mood.