Modality as part of language is an extremely complex phenomenon whose definition and description have been one of the most persistent problems for linguists. The concept of modality in ordinary language includes attitudes which are similar to, but not identical with the logical, epistemic and deontic modalities. It includes feelings and emotions as well as other concepts that do not exist in modal logic, there for, natural language modality should not be confused with logical modality. The complexity of this phenomenon is so great that there is little agreement in the literature as to how modality should be defined. But we all agree that „modality expresses the attitude of the speaker towards what he is saying” (T. Dutescu and Coliban, „Grammatical Categories of English”, p. 275).
In other words, as Loreto Todd and Ian Hancock say, „modality refers to the attitudes expressed by a speaker towards the statement or preposition being made.” (Loreto Todd/Ian Hancock, „International English Usage”, p. 22). They also add that such attitudes may express ability, compulsion, desire, insistence, obligation, permission, probability, possibility, willingness and uncertainty.
Certain grammar postulate a modality component in their organization. In Filmore’s „Case Grammar” , for example, every sentence is decomposed into a modality constituent and a preposition, that is a set of relationship involving verb phrases and noun phrases, not different in essence from the logical notion of proposition.
Sentence → Modality + Proposition
What is important in this view point is the idea of separating modal meaning from the basic meaning. Although modality is often characterized as a verbal category, since it is at the level of the verb phrase, modality applies to the whole statement. So, it should be taken as a sentence category.
It is relevant to say that modality can be seen from a semantic point of view. Wilfried Rathay tries to understand whether modality constitutes a grammatical category, i.e. a morpho-syntactic category, or whether it should be looked upon as a semantic phenomenon. He considers that modality has to be regarded as one of the main features of sentence or, as some linguists maintain, as an obligatory characteristic of every sentence. (cf. Gordon/Krilova, Pantilov, Mühlner).
There is, however, divergent opinions about what be included under this term. In some cases, only the general feature is taken to be essential: „the relationship between the statement affirmed in the sentence and reality as established by the speaker.” Other linguists emphasize the twofold aspect of the notion „modality” and differentiate between: a) „the relationship of the content of the sentence to reality (as regarded by the speaker)” and b) „the attitude of the speaker towards the content of the sentence.” (cf. Achmanova).
Sometimes, a third aspect is mentioned which is supposed to specify „the relationship of the subject of an action, process or state towards this action, process or state.” (modality expressed by modal verbs: He can swim, He must do it.) (cf. Sommerfeldt, Schmidt, Zakotova)
The first aspect is quite often referred to as „objective or basic modality and it is expressed by the morphological category „mood” (indicative, subjunctive, imperative)”. So, the main distinction should be drawn between „real” and „unreal” events. The second aspect is usually called „subjective modality”. It permits the speaker to evaluate the content of a sentence in a particular way. In contrast to objective modality, it is regarded as optional, i.e. a sentence may or may not contain an element of subjective modality.
Halliday reduces the term „modality” to „the speaker’s assessment of the probability of what he is saying or the extent to which he regards it as self-evident.” The meanings of the modals such as permission, ability, obligation, compulsion etc. are considered to belong to a different system, which he calls „modulation”.
Sometimes, modality is identified with the „communicative intention” of the speaker, i.e. modal types are set up according to the main types of sentences with respect to their function in a particular communication situation (assertive, interrogative and imperative modality). This view is rejected by many linguists who maintain that the communicative intention of the speaker towards the interlocutor is something different from the relationship between the content of a sentence and reality.
I would add here Hemeren’s point of view. He distinguishes three main types of modality: internal, external and neutral.
In the „internal modality” the constituent expressing modality and the following verb share the same subject. Consequently, the relationship may be illustrated thus:
John able (John go).
In the surface structure this may be realized as, for instance:
John can go. or John’s ability to go.
In the “external modality” the constituent expressing modality and the following verb have different subjects, as in: Dick permits John (John go). This can be realized as:
“You may go”, said Dick to John.
Finally, in the “neutral modality” the subject of the constituent expressing modality is the clause consisting of the following verb and its subject, as in: Probable (John go). where John goes is the subject of probable. This can be realized as:
That John will go is probable. or the probability of John going.
Most of the traditional grammars do not give a coherent presentation of the category of modality. Modal types and meanings are usually described isolated from each other according to the grammatical categories or parts of speech they belong to (mood, modal verbs, modal nouns, etc.). The way in which transformational generative grammars have so far dealt with questions of modality seems even less satisfactory. Earlier versions of TG enumerate some modals as elements of the auxiliary constituent derived from. Others, such as Roberts or Catell say a little more about the modals, but do not touch upon any fundamental questions. Others either deal with questions concerning the classification of the modals or try to present a few semantic features for certain modal verbs.