The present study aims to show the diachronic change of the English present perfect progressive from the simple present tense (SP). I assert that SP is the psychological present tense describing the imperfective (unfinished) present process of the speaker’s/writer’s brain/mind. In accord with this, as the mind or psychology of the native speaker/writer changes, the usage of SP changes, and one example of this is the present perfect progressive in Present-Day English (PE). In Old English (OE), Middle English and Early Modern English, SP is used instead of the present perfect progressive, whereas the present perfect progressive is used in PE as a result of the change of the psychology of SP and the gradual change and completion of the English auxiliary phrase. In addition to the change of psychology of the speaker, English has adopted the present perfect progressive since ME as a result of the gradual change and completion of the auxiliary phrase. It is proposed that the gradual change and completion of the English auxiliary phrase from OE to PE has caused the motivation for the change of the psychology of the speaker of English in cooperation to employ the present perfect and then the present perfect progressive instead of the SP.