In Tagalog grammar, the Tense Theory is crucial in understanding how actions or events are expressed in terms of time. Tagalog has three tenses: past, present, and future. Each tense is determined by the affixes added to the verb root.

To express past actions, the verb root is combined with the affix “na-” or “nag-” depending on the verb type. For example, “kumain” (ate) becomes “kumain na” (already ate) or “kumain nag-” (ate). Meanwhile, the present tense is indicated by the absence of any affixes. So “kumain” (ate) can mean “eat” in the present context. Lastly, for future actions, the verb root is combined with the affix “mag-” or “mang-” depending on the verb type. Thus, “kain” (eat) becomes “magkain” (will eat) or “mangkain” (will eat).

It is important to note that Tagalog has a flexible notion of time, allowing speakers to indicate specific time frames through contextual cues or time adverbials. Nevertheless, a solid understanding of the Tense Theory is fundamental in constructing grammatically correct sentences and communicating effectively in Tagalog.