Perfect Progressive theory in Lithuanian grammar refers to a specific tense form that expresses an ongoing action that was completed at a particular point in the past. It is a combination of the perfect aspect and the progressive aspect.

In Lithuanian, the perfect progressive tense is formed by combining the past tense of the verb “būti” (to be) with the participle of the main verb and the particle “buvo” (had been). The participle is formed by adding a suffix, depending on the verb type, to the base form of the verb. For example, the participle of the verb “kalbėti” (to speak) is “kalbėjęs/kalbėjusi/kalbėjusi/kalbėję”.

The perfect progressive tense is used to describe an action that started in the past and continued until another point in the past. It emphasizes the duration and continuity of the action. For example, “Aš buvau kalbėjęs su jais” means “I had been speaking with them.” It indicates that the speaking had started in the past and continued until a specific point, without mentioning when it ended.