[3] Therein, what is past form (rūpa)?
That form which is past, ceased, gone, changed, come to an end, utterly come to an end; which, having arisen, has gone; which is past and is included in the past portion — namely, the four primary elements (mahābhūta) and the form derived from the four primary elements: this is called past form.
Therein, what is future form?
That form which is not born, not become, not begotten, not produced, not fully produced, not manifest, not arisen, not fully arisen, not risen up, not fully risen up; which is future and is included in the future portion — namely, the four primary elements and the form derived from the four primary elements: this is called future form.
Therein, what is present form?
That form which is born, become, begotten, produced, fully produced, manifest, arisen, fully arisen, risen up, fully risen up; which is present and is included in the present portion — namely, the four primary elements and the form derived from the four primary elements: this is called present form.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.