Modals are auxiliary verbs that function as building blocks in different verb constructions. Their position in the sentence indicates whether it is a question or statement. There are two types of modals: non-inflecting (modal) verbs that only occur with main verbs, such as can, may, must. Be, have, and do inflect for person and tense and can also function as main verbs. Modals have limited forms compared to be and have. Common paraphrases are used when modals are missing forms, such as "be able to" for can and may, "have to" for must. Modals can have multiple meanings depending on context.