yataḥ samprāptakāritro vartamāna ucyate, uparatakāritro 'tītaḥ, aprāptakāritro 'nāgata ityadhvānaḥ kāritreṇa vyavasthitāḥ /
Because that which has obtained activity is called "present," that whose activity has ceased is "past," and that which has not obtained activity is "future" - thus the states are established through activity.