It may refer to a distinct verb form that expresses the conditional set of circumstances proper in the dependent clause or protasis (e.g. in Turkish or Azerbaijani[a]), or which expresses the hypothetical state of affairs or uncertain event contingent to it in the independent clause or apodosis, or both (e.g. in Hungarian or Finnish[b]).
Examples are the English and French conditionals (an analytic construction in English,[c] but inflected verb forms in French), which are morphologically futures-in-the-past,[1] and of which each has thus been referred to as a "so-called conditional"[1][2] (French: soi-disant conditionnel[3][4][5]) in modern and contemporary linguistics (e.g. French je chanterais, from Late Latin cantāre habēbam, in si vous me le permettiez, je chanterais, "if you allowed me to do so, I would sing" [so-called conditional] vs. j'ai dit que je chanterais, "I said that I would sing" [future-in-the-past]).
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").
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.
In French, Spanish, Portuguese, Catalan and Occitan, the conditional endings come from the imperfect of Latin habēre.
For example, in the first person singular: 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 § Proclisis, enclisis, and mesoclisis).
Old Italian had originally three different forms of conditional:[10] Only the Tuscan form survives in modern Italian: The second and third types have slowly disappeared remaining until the 19th century in some poetic composition for metric needs.
[10] Romanian uses a periphrastic construction for the conditional, e.g. 1sg aș, 2sg ai, 3sg/pl ar, 1pl am, 2pl ați + cânta 'sing'.
The modal clitic mixes forms of Latin habēre: Old Romanian, on the other hand, used a periphrastic construction with the imperfect of vrea 'to want' + verb, e.g. vrea cânta 'I would sing', vreai cânta 'you would sing', etc.
The Conditional is also one of the two Portuguese tenses which demand mesoclisis when proclisis is forbidden – since enclisis is always considered ungrammatical.
Polish forms the conditional mood in a similar way to Russian, using the particle by together with the past tense of the verb.
In the present tense, the marker appears right after the verb stem and just before the affix of the verbal person.
The conditional mood is often used with potential suffixes attached to the verb stem (-hat/-het), and the two are therefore often confused.