Grammatical category of Mood.
The meaning of this category is the attitude of the speaker or writer towards the content of the sentence, whether the speaker considers the action real, unreal, desirable, necessary, etc. It is expressed in the form of the verb.
There are three moods in English - the indicative mood, the imperative mood and the oblique mood.
The indicative mood form shows that what is said must be regarded as a fact, as something which has occurred or is occurring at the moment of speaking or will occur in the future. It may denote actions with different time-reference and different aspective characteristics. Therefore the indicative mood has a wide variety of tense and aspect forms in the active and passive voice.
The imperative mood expresses a command or a request to perform an action addressed to somebody, but not the action itself. As it does not actually denote an action as a real act, it has no tense category. The unfulfilled action always refers to the future. Aspect distinctions and voice distinctions are not characteristic of the imperative mood, although forms such as, be writing, be warned sometimes occur. This form is always addressed to the second person.
The oblique mood expresses non-facts: unreal or hypothetical actions or states. A hypothetical action or state may be viewed upon as desired, necessary, possible, supposed, imaginary, or contradicting reality.
In Old English the oblique mood was expressed by a special system of forms with a special set of inflections, different from those of the indicative. In the course of time most of the inflections were lost, and the difference between the forms of the oblique and those of the indicative has almost disappeared. In Modern English there remain only two synthetic forms of the old regular system of the subjunctive, which differ from the forms of the indicative.
Subjunctive I coincides with the plain verb stem for all persons in both the singular and the plural. It denotes a hypothetical action referring to/the present or future. Of these surviving forms only be is always distinct from the indicative forms and is therefore rather current.
Subjunctive II refers the hypothetical action to the present, future or past and shows that it contradicts reality. The non-factual past indefinite and past continuous are used to denote hypothetical actions in the present or future. The non-factual past perfect and past perfect continuous denote hypothetical actions in the past.
Most of the later formations are analytical, built by means of the auxiliaries which developed from the modal verbs should and would, plus any form of the infinitive.
According to their use and function analytic oblique forms may be divided into two groups.
The Conditional Mood is formed by means of would + infinitive for all persons, both singular and plural. This form denotes an unreal action the unreality of which is due to the absence of necessary conditions. It may be used both in simple and complex sentences.
The Suppositional Mood is formed by means of should+ infinitive for all persons, both singular and plural. This mood represents the action as problematic, but not contradicting reality. This form expresses necessity, suggestion, advice, supposition.
In conclusion, it must be mentioned that the whole system of the English subjunctive mood is not stable; it is still developing and the use of forms fluctuates a lot: for example, the form was is often used instead of were in the third person singular in subjunctive II (If he was here…), the auxiliaries should and would are often interchangeable, etc. In colloquial speech the semantic and formal contrasts between the indicative, the past subjunctive and the modal subjunctive are often neutralized, e.g.: It is impossible that he is right/ that he should be right/ that he be right; neutralization is also natural in reported speech in the past, e.g.: She thought that if she tried harder she would get the job.