A modal adverb is a specific type of adverb that adds additional meaning to modal verbs. Modal verbs are verbs that express modality, which has to do with properties such as possibility, obligation, and emphasis. Modal adverbs modify specific verbs that consist of a linking verb (verb of being) and sometimes another verb, such as can, could, may, might, must, shall, should, will, and would. They are used to say something about possibility, obligation, and emphasis, and cannot be negated or used in questions. Examples of modal adverbs include "surely," "really," and "certainly".