The Perfect Progressive Theory, or thì Hiện tiếp hoàn thành in Vietnamese, describes an action that started in the past, continued up until the present, and is still ongoing. This tense is formed by using the auxiliary verb đã (have/has) before the main verb, and the auxiliary verb đang (in the process of) after the main verb.

For example, to say “I have been studying Vietnamese for two years,” we would say “Tôi đã học tiếng Việt hai năm rồi đó.” Here, đã indicates the action started in the past, học tiếng Việt is the main verb, and đang after rồi indicates that the action is still ongoing.

The Perfect Progressive Theory is used to express an action that is still happening or has just finished. It is often used to talk about personal experiences, habits, or actions that have a direct impact on the present. It is an important tense to master in order to convey accurate and precise information in Vietnamese.