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Every language has a formula for the unreal. The Indigenous languages of the Pacific Northwest have as many as five levels of "unreality."
Main irrealis moods 
E.g.: "If I loved you..." / "May I love you"
The subjunctive mood, sometimes called conjunctive mood, has several uses in dependent clauses. Examples include discussing hypothetical or unlikely events, expressing opinions or emotions, or making polite requests (the exact scope is language-specific). A subjunctive mood exists in English, but it often is not obligatory. Example: "I suggested that Paul eat an apple", Paul is not in fact eating an apple. Contrast this with the sentence "Paul eats an apple", where the verb "to eat" is in the present tense, indicative mood. Another way, especially in British English, of expressing this might be "I suggested that Paul should eat an apple", derived from "Paul should eat an apple."
Other uses of the subjunctive in English, as in "And if he be not able to bring a lamb, then he shall bring for his trespass..." (KJV Leviticus 5:7), have become archaic. Statements such as "I shall ensure that he leave immediately" often sound overly formal, and often have been supplanted by constructions with the indicative, such as "I shall ensure that he leaves immediately".
The subjunctive mood figures prominently in the grammar of the Romance languages, which require this mood for certain types of dependent clauses. This point commonly causes difficulty for English speakers learning these languages.
In certain other languages, the dubitative or the conditional moods may be employed instead of the subjunctive in referring to doubtful or unlikely events (see the main article).
E.g.: "I would love you."
The conditional mood (abbreviated COND) is used to speak of an event whose realization is dependent upon another condition, particularly, but not exclusively, in conditional sentences. In Modern English, it is a periphrastic construction, with the form would + infinitive, e.g. I would buy. In other languages, such as Spanish or French, verbs have a specific conditional inflection. This applies also to some verbs in German, in which the conditional mood is conventionally called Konjunktiv II, differing from Konjunktiv I. Thus, the conditional version of "John eats if he is hungry" is:
- John would eat if he were hungry, in English;
- Johannes äße, wenn er hungrig wäre, in German;
- Jean mangerait s'il avait faim, in French;
- Juan comería si tuviera hambre, in Spanish.
- Giovanni mangerebbe se avesse fame, in Italian;
Johannes würde essen, wenn er Hunger hätte is also acceptable in German.
In the Romance languages, the conditional form is used primarily in the apodosis (main clause) of conditional clauses, and in a few set phrases where it expresses courtesy or doubt. The main verb in the protasis (dependent clause) is either in the subjunctive or in the indicative mood. However, this is not a universal trait: among others in German (as above) and in Finnish the conditional mood is used in both the apodosis and the protasis. A further example is the sentence "I would buy a house if I earned a lot of money", where in Finnish both clauses have the conditional marker -isi-: Ostaisin talon, jos ansaitsisin paljon rahaa. In Polish the conditional marker -by also appears twice: Kupiłbym dom, gdybym zarabiał dużo pieniędzy. Because English is used as a lingua franca, a similar kind of doubling of the word would is a fairly common way to misuse an English language construction.
In English, too, the would + infinitive construct can be employed in main clauses, with a subjunctive sense: "If you would only tell me what is troubling you, I might be able to help".
The optative mood expresses hopes, wishes or commands and has other uses that may overlap with the subjunctive mood. Few languages have an optative as a distinct mood; some that do are Albanian, Ancient Greek, Sanskrit, Finnish, and all forms of the Persian language (Avestan, Old Persian, Middle Persian, New Persian).
In Finnish, the mood may be called an "archaic" or "formal imperative", even if it has other uses; nevertheless, it does express formality at least. For example, the ninth Article of the Universal Declaration of Human Rights begins with Älköön ketään pidätettäkö mielivaltaisesti, "Not anyone shall be arrested arbitrarily", where älköön pidätettäkö "shall not be arrested" is the optative of ei pidätetä "is not arrested". (Also, using the conditional mood -isi- in conjunction with the clitic -pa yields an optative meaning, e.g. olisinpa "if I only were". Here, it is evident that the wish is not, and probably will not be fulfilled.)
In Sanskrit, the optative is formed by adding the secondary endings to the verb stem. The optative, as other moods, is known in active voice and medium voice. Examples: bhares "may you bear" (active) and bharethaas "may you bear [for yourself]" (medium). The optative may not only express wishes, requests and commands, but also possibilities, e.g. kadaacid goshabdena budhyeta "he might perhaps wake up due to the bellowing of cows"., doubt and uncertainty, e.g. katham vidyaam Nalam "how would I be able to recognize Nala?" The optative may further be used instead of a conditional mood.
The jussive mood (abbreviated JUS) expresses plea, insistence, imploring, self-encouragement, wish, desire, intent, command, purpose or consequence. In some languages, this is distinguished from the cohortative mood in that the cohortative occurs in the first person and the jussive in the second or third. It is found in Arabic, where it is called the مجزوم majzūm. The rules governing the jussive in Arabic are somewhat complex.
The potential mood (abbreviated POT) is a mood of probability indicating that, in the opinion of the speaker, the action or occurrence is considered likely. It is used in Persian, Finnish, Japanese, in Sanskrit and in the Sami languages. (In Japanese it is often called something like tentative, since potential is used to refer to a voice indicating capability to perform the action.)
In Finnish, it is mostly a literary device, as it has virtually disappeared from daily spoken language in most dialects. Its suffix is -ne-, as in *men + ne + e → mennee "(s/he/it) will probably go". Some kinds of consonant clusters simplify to geminates. This simplification occurs progressively (*rne → rre) with the resonant consonants l, r, and s, and regressively with stops (*tne → nne) and is meant to prevent the violation of phonotactical rules concerning sonority hierarchy. For example, korjata → *korjat + ne + t → korjannet "you will probably fix", or tulla → *tul + ne + e → tullee "s/he/it will probably come". The potential mood can be used only in present and perfect tenses. The verb ole- "be" is replaced by lie, so that "(it) is probably" is lienee (not *ollee). Thus, in the perfect tense, which is formed with an auxiliary verb, the auxiliary verb lie is used instead of ole- as liene-, e.g. lienet korjannut "you have probably fixed" (not *ollet korjannut). In spoken language, the word kai "probably" is used instead, e.g. se kai tulee "he probably comes", instead of hän tullee.
The imperative mood expresses direct commands, requests, and prohibitions. In many circumstances, using the imperative mood may sound blunt or even rude, so it is often used with care. Example: "Paul, do your homework now". An imperative is used to tell someone to do something without argument.
In English, second person is implied by the imperative except when first-person plural is specified, as in "Let's go" ("Let us go").
The prohibitive mood, the negative imperative may be grammatically or morphologically different from the imperative mood in some languages. It indicates that the action of the verb is not permitted, e.g. "Do not go!" (archaically, "Go not!")
In English, the imperative is sometimes used to form a conditional sentence: e.g. "Go eastwards a mile, and you will see it" means "If you go eastward a mile, you will see it".
Less common irrealis moods 
Whereas the optative expresses hopes, the desiderative mood expresses wishes and desires. Desires are what we want to be the case; hope generally implies optimism toward the chances of a desire's fulfillment. If someone desires something but is pessimistic about its chances of occurring, then one desires it but does not hope for it. Few languages have a distinct desiderative mood; some that do are Sanskrit and Japanese.
In Japanese the verb inflection -tai expresses the speaker's desire, e.g. watashi wa asoko ni ikitai "I want to go there". This form is treated as a pseudo-adjective: the auxiliary verb garu is used by dropping the end -i of an adjective to indicate the outward appearance of another's mental state, in this case the desire of a person other than the speaker (e.g. Jon wa tabetagatte imasu "John wants to eat").
In Sanskrit, the infix -sa-, sometimes -isa-, is added to the replicated root, e.g. jijiivishati "he wants to live" instead of jivati "he lives". The desiderative in Sanskrit may also be used as imminent: mumuurshati "he is about to die".
The dubitative mood is used in Ojibwe, Turkish, and other languages. It expresses the speaker's doubt or uncertainty about the event denoted by the verb. For example, in Ojibwe, Baawitigong igo ayaa noongom translates as "he is in California today." When the dubitative suffix -dog is added, this becomes Baawitigong igo ayaadog noongom, "I guess he must be in California.
E.g.: "I could love you [if...]"
E.g.: There is no exact English example, although it could be translated as: "[Even] If I loved you [...]"
The presumptive mood is used in Romanian to express presupposition or hypothesis, regardless the fact denoted by the verb, as well as other more or less similar attitudes: doubt, curiosity, concern, condition, indifference, inevitability. For example, acolo s-o fi dus "he might have gone there" shows the basic presupposition use, while the following excerpt from a poem by Eminescu shows the use both in a conditional clause de-o fi "suppose it is" and in a main clause showing an attitude of submission to fate le-om duce "we would bear".
- De-o fi una, de-o fi alta... Ce e scris și pentru noi,
- Bucuroși le-om duce toate, de e pace, de-i război.
- Be it one, be it the other... Whatever fate we have,
- We will gladly go through all, be it peace or be it war
The permissive mood indicates that the action is permitted by the speaker.
The admirative mood (abbreviated MIR) is used to express surprise, but also doubt, irony, sarcasm, etc. In Indo-European languages, the admirative, unlike the optative, is not one of the original moods, but a later development. Admirative constructs occur in Balkan Slavic (Bulgarian and Macedonian), Tosk Albanian, and Megleno-Romanian. A form of the admirative, derived from the Albanian pattern, can be found in Frasheriote Arumanian.
The hortative mood (alternatively, "hortatory") is used to express plea, insistence, imploring, self-encouragement, wish, desire, intent, command, purpose or consequence. It does not exist in English, but phrases such as "let us" are often used to denote it. In Latin, it is interchangeable with the jussive.
The eventive mood is used in the Finnish epic poem Kalevala. It is a combination of the potential and the conditional. It is also used in dialects of Estonian. In Finnish, there are theoretically forms such as kävelleisin "I would probably walk".
E.g.: "Will you love me?"
Precative (abbreviated PREC) mood is a grammatical mood which signifies requests, e.g. "Will you pass me the salt?"
The volitive mood (abbreviated VOL) is used to indicate the speaker's desires, wishes, or fears.
Inferential or renarrative 
The inferential mood (abbreviated INFER or INFR) is used to report a nonwitnessed event without confirming it, but the same forms also function as admiratives in the Balkan languages in which they occur. The inferential mood is used in some languages such as Turkish to convey information about events, which were not directly observed or were inferred by the speaker. When referring to Bulgarian and other Balkan languages, it is often called renarrative mood; when referring to Estonian, it is called oblique mood. The inferential is usually impossible to be distinguishably translated into English. For instance, indicative Bulgarian той отиде (toy otide) and Turkish o gitti will be translated the same as inferential той отишъл (toy otishal) and o gitmiş — with the English indicative he went. Using the first pair, however, implies very strongly that the speaker either witnessed the event or is very sure that it took place. The second pair implies either that the speaker did not in fact witness it take place, that it occurred in the remote past or that there is considerable doubt as to whether it actually happened. If it were necessary to make the distinction, then the English constructions "he must have gone" or "he is said to have gone" would partly translate the inferential.
- Gonda, J., 1966. A concise elementary grammar of the Sanskrit language with exercises, reading selections, and a glossary. Leiden, E.J. Brill.
- Van Der Geer, AAE. 1995. Samskrtabhasa B1, cursus Sanskrit voor beginners and Samskrtabhasa B2, cursus Sanskrit voor gevorderden. Leiden: Talen Instituut Console
- Ontario Curriculum Support Document for the Teaching of Language Patterns
- Loos, Eugene E.; Susan Anderson; Dwight H. Day, Jr.; Paul C. Jordan; J. Douglas Wingate. "What is permissive mood?". Glossary of linguistic terms. SIL International. Retrieved 2009-12-28.
- For a more precise rendering, it would be possible to also translate these as "he reportedly went" or "he is said to have gone" (or even "apparently, he went") although, clearly, these long constructions would be impractical in an entire text composed in this tense.
- deontic modality
- epistemic modality
- irrealis modality: (subjunctive mood)
- Greek tenses