The Perfect Progressive theory in Swahili grammar describes the action that has been ongoing in the past and it is still ongoing in the present. It is formed using the verb tense prefix “ME-” or “ME-NA-” followed by the verb stem, and finally the verb tense suffix “-KI-.

For example, the verb “kuandika” (to write) in the perfect progressive tense would be “nimekuwa ninaandika” which translates to “I have been writing.”

In this tense, the prefix “ME-” indicates past tense, the infix “-NA-” indicates the ongoing nature of the action, and the suffix “-KI-” indicates the perfect progressive tense.

It is important to note that the verb stem remains the same throughout the tense while the prefix, infix, and suffix are the components that change to form the tense.

The Perfect Progressive theory is useful in expressing actions that started in the past and are still continuing in the present. It adds depth to our understanding of the timeline of events in Swahili.