What Are Modals and Semi-modals?
Modal verbs (also called modals or modal auxiliary verbs), are special verbs that give additional information about the function of the main verb that follows them. Modals have a wide variety of communicative functions (i.e. modality).
Some verbs share only some of the characteristics of the modals. These verbs are called semi-modals (or pseudo-modals or quasi-modals).