This paper introduces the key issues of scalar implicature. There are many scalars in languages. These scalars establish many possible implicatures. Studies show that the Cooperative Principle of Grice could not explain all the different phenomena of scalar implicatures. Meanwhile, the Relevance Principle of Sperber and Wilson tmns out to be an effective tool. Many subsequent researchers such as Horn and Lewinson and others have modified Grice's theory. This paper develops some specific structures of empty words in Vietnamese. These play a key role in conveying scalar implicatures, especially those with extreme implications.