VOA慢速英语:Would You Like to Learn About Modal Auxiliaries?

modal auxiliary – n. grammar a verb (such as can, could, shall, should, ought to, will, or would) that is usually used with another verb to express ideas such as possibility, necessity, and permission

form class – n. large, open classes of words that provide the lexical content of the language

structure class – n. small, closed classes of words that explain the grammatical relationships of the form classes.

master - v. to learn (something) completely; to get the knowledge and skill that allows you to do, use, or understand (something) very well

context – n. the situation in which something happens; the group of conditions that exist where and when something happens

unrealized – adj. not effected, accomplished, or fulfilled (not realized)

polite – adj. socially correct or proper