All human languages have modality, or ways to express attitudes such as doubt, uncertainty or unreality using morphological or syntactic forms. Some languages have numerous ways to express mood, such as Nenets, spoken in Russia's far north, which has 16 moods. Other languages, such as English, have only three or four moods. Although most linguistic studies of modality focus on epistemic grammatical mood, which refers to the ways speakers express uncertainty and unreality using specific structures and forms, other kinds of modalities might exist. The interrogative mood, which includes structures related to asking questions, can be included in this group, although in some ways, it differs from other expressions of mood found in languages around the world.
Grammatical mood is a set of verbal inflections — expressed either as syntactical constructions or inflections of the verb form itself — that add emotional color to an utterance. In English, for example, the subjunctive mood allows speakers to make assertions about the reality or unreality of situations in sentences such as, "If I had known you were going to be late, I'd have waited." Since English is largely not an inflected language, verb structures such as the past perfect and the conditional "would" express that the situation is in the past, so it has no chance of becoming real in the speaker's present time. Other types of modalities include the indicative mood, which asserts a fact, such as the sentence, "He is here;" and the imperative, which is for commands or requests, such as the sentence, "Come here."
Some linguists question whether sets of structures for asking questions — an interrogative mood — can be considered a true mood. These structures can include variations in syntactic patterns, such as inverting elements in the sentence. In some languages, such as English, subject-verb order can be reversed in questions, such as the statement "he is here" becoming the question, "Is he here?"
Questions can be created through inflection alone, conveying disbelief or a need for confirmation, as in, "You're coming to the party?" When questions involve grammatical polarity, or yes-or-no questions, they might have other kinds of grammatical features to express the interrogative, such as the addition of tag questions, as in, "You're coming, aren't you?" They also might use particles, as in, "He's very stupid, no?"
Interrogative structures appear to be similar semantically across language groups, although their expression in linguistic forms varies widely. Only a few languages, such as Irish and Scots Gaelic, Welsh and Korean have a true interrogative mood characterized by specific verbal inflection, such as the addition of particles or a change in verb form. The use of question structures to express moods such as uncertainty about an outcome, verifying an assumption, and confirming a truth, however, can be found in languages worldwide. This suggests the presence of an interrogative mood in a broader sense than verb morphology alone.