It is a conceptual category expressing the purposefulness of speech, the relationship of a speaker to the content of his utterance, and the relationship of the content of the utterance to reality
Modality may signify affirmation, command, desire, permission, truth, and unreality. It can be expressed by three categories of forms expressing modality: I. Modal verbs II. Modal words (perhaps, likely) III. Intonational means
Modal verbs unlike other verbs, do not denote actions or states, but only show the attitude of the speaker towards the action expressed by the infinitive in combination with which they form compound modal predicates.
Can Could May Might Must Shall Should Will Would
Position of modal verbs Modal verbs always appear in the first position at the beginning of the verb phrase in English. Unlike other verbs they do not show tense or number