The conditional mood is a grammatical mood used to express a proposition whose validity is dependent on some condition, possibly counterfactual. It thus refers to a distinct verb form that expresses a hypothetical state of affairs, or an uncertain event, that is contingent on another set of circumstances. An example of a verb in the conditional mood is the French aimerait, meaning "would love" (from the verb aimer, "to love").
Conditional mood often refers to an inflected verb form, like the example just given. However the term is also sometimes used in relation to an analytic construction that performs the same function. Thus a construction like the English would love will sometimes be described as representing the conditional mood. In some informal contexts, such as language teaching, it may be called the "conditional tense".
The conditional mood is generally found in the independent clause (apodosis) of a conditional sentence, namely the clause that expresses the result of the condition, rather than the dependent clause (protasis) expressing the condition. The protasis will often use a different verb form, depending on the grammatical rules of the language in question, such as a past tense form or the subjunctive mood. This is exemplified by the English sentence "If you loved me you would support me" – here the conditional would support appears in the apodosis, while the protasis (the condition clause) uses instead the simple past form loved.
Not every conditional sentence involves the conditional mood (and some languages do not have a conditional mood at all). For example, in the sentence "If I win, he will be disappointed", the conditional circumstance is expressed using the future marker will. Also a conditional verb form may have other uses besides expressing conditionality; for example the English would construction may also be used for past habitual action ("When I was young I would happily walk three miles to school every day"), or with future-in-the-past meaning.
Conditional mood can be denoted by the glossing abbreviation COND. Some languages distinguish more than one conditional mood; the East African language Hadza, for example, has a potential conditional expressing possibility, and a veridical conditional expressing certainty.
This article describes the formation of the conditional forms of verbs in certain languages. For fuller details of the construction of conditional sentences, see Conditional sentence (and for English specifically, English conditional sentences).
Germanic languages 
English does not have an inflective (morphological) conditional mood, except in as much as the modal verbs could, might, should and would may in some contexts be regarded as conditional forms of can, may, shall and will respectively. What is called the English conditional mood (or just the conditional) is formed periphrastically using the modal verb would in combination with the bare infinitive of the main verb. (Occasionally should is used in place of would with a first person subject – see shall and will. Also the aforementioned modal verbs could, might and should may replace would in order to express appropriate modality in addition to conditionality.)
English has three types of conditional sentences, which may be desribed as factual ("conditional 0": "When I feel well, I sing"), predictive ("conditional I": "If I feel well, I will sing"), and speculative ("conditional II" or "conditional III": "If I felt well, I would sing" or "If I had felt well, I would have sung"). As in many other languages, it is only the speculative type that causes the conditional mood to be used.
Conditionality may be expressed in several tense–aspect forms. These are the simple conditional (would sing), the conditional progressive (would be singing), the conditional perfect (would have sung), and conditional perfect progressive (would have been singing). For the uses of these, see Uses of English verb forms. The conditional simple and progressive may also be called the present conditional, while the perfect forms can be called past conditional.
For details of the formation of conditional clauses and sentences in English, see English conditional sentences.
In German, two verbal constructions express conditionality:
- Konjunktiv Futur II (Konjunktiv II, Futur I) corresponds to English's present conditional. It is formed with the auxiliary verb werden in its subjunctive form, plus the infinitive:
- Ich würde singen ("I would sing")
- Konditional Perfekt (Konjunktiv II, Futur II) corresponds to English's past conditional. It is a form of the perfect construction: it uses a form of the auxiliary haben or sein (depending on the main verb) together with the past participle of the main verb. The auxiliary in this case takes past subjunctive form: hätte/st/t/n (in the case of haben) or wäre/st/t/n (in the case of sein.
- Ich hätte gesungen ("I had [subjunctive] sung", i.e. "I would have sung")
- Sie wären gekommen ("They were [subjunctive] come", i.e. "They would have come")
For more information, see German conjugation.
Romance languages 
While Latin used the indicative and subjunctive in conditional sentences, most of the Romance languages developed a conditional paradigm. The evolution of these forms (and of the innovative Romance future tense forms) is a well-known example of grammaticalization, whereby a syntactically and semantically independent word becomes a bound morpheme with a highly reduced semantic function. The Romance conditional (and future) forms are derived from the Latin infinitive followed by a finite form of the verb habēre. This verb originally meant "own/possess" in Classical Latin, but in Late Latin picked up a grammatical use as a temporal/modal auxiliary. The fixing of word order (infinitive + auxiliary) and the phonological reduction of the inflected forms of habēre eventually led to the fusion of the two elements into a single synthetic form.
A trace of the historical presence of two separate verbs can still be seen in the possibility of mesoclisis in conservative varieties of European Portuguese, where an object pronoun can appear between the verb stem and the conditional ending (e.g. cantá-lo-ia, see Portuguese personal pronouns and possessives). Italian had a similar form, but it also developed conditional verbs based on the perfect forms of habēre, and these are the forms that survive in modern Italian:
- Lat. cantāre habuit > *cantare ebbe > It. canterebbe
Romanian uses an analytic construction for the conditional, e.g. 1sg aș cânta. (The auxiliary element may derive ultimately from Latin habēre, or it could be a reduced form of a volitional verb a vrea or a voi.)
Slavic languages 
- Я хотел петь ja khotel pet ("I wanted to sing")
- Я хотел бы петь ja khotel by pet ("I would like, literally would want, to sing")
Polish forms the conditional (or subjunctive) mood in a similar way to Russian, using the particle by together with the past tense of the verb. This is an enclitic particle, which often attaches to the first stressed word in the clause, rather than following the verb. It also takes the personal endings (in the first and second persons) which usually attach to the past tense. For example:
- śpiewałem/śpiewałam ("I sang", masculine/feminine)
- śpiewał(a)bym, or ja bym śpiewał(a) ("I would sing")
There is also a past conditional, which also includes the past tense of the copular verb być, as in był(a)bym śpiewał(a) ("I would have sung"), but this is rarely used; the ordinary conditional is normally used instead.
For details see Polish verbs.
- Mead, Hayden; Stevenson, Jay (1996), The Essentials of Grammar, New York: Berkley Books, p. 55, ISBN 978-0-425-15446-5, OCLC 35301673
- Weisberg, Valerie H. (1986), English Verbs, Every Irregular Conjugation, Van Nuys, California: V.H. Weisberg, p. 108, ISBN 978-0-9610912-5-5, OCLC 13770299
- Listen, Paul (2005), The big yellow book of German verbs, Chicago: McGraw-Hill, p. 19, ISBN 978-0-07-146955-5, OCLC 61370368
- Listen, Paul (2005), The big yellow book of German verbs, Chicago: McGraw-Hill, p. 28, ISBN 978-0-07-146955-5, OCLC 61370368
Further reading 
- Aski, Janice M. 1996. "Lightening the Teacher's Load: Linguistic Analysis and Language Instruction". Italica 73(4): 473-492.
- Benveniste, E. 1968. "Mutations of linguistic categories". In Y. Malkiel and W.P. Lehmann (eds) Directions for historical linguistics, pp. 83–94. Austin and London: University of Texas Press.
- Joseph, Brian D. 1983. The synchrony and diachrony of the Balkan infinitive: a study in general, areal, and historical linguistics. Cambridge: Cambridge University Press. ISBN 0-521-27318-8.