Alfred North Whitehead, answered from the texts and cited to the page.
Perishing is not annihilation. When an actual occasion reaches its satisfaction — that terminal unity in which every element of the universe receives either a positive or a negative prehension, and indetermination has wholly evaporated into complete determinateness — it passes from the immediacy of being into what I call the not-being of immediacy.1
But not-being of immediacy is not nothing. The occasion becomes stubborn fact, and stubborn fact endures. Pereunt et imputantur — they perish, and they are put to the account.2 This is what I mean by objective immortality: the perished occasion does not vanish; it becomes a datum available for prehension by every subsequent becoming. A pure physical prehension is precisely how a new occasion, in its own immediacy of becoming, absorbs another occasion that has passed into this objective immortality.3
The past lives in the present through that absorption. It is causation; it is memory; it is perception of derivation; it is emotional conformation to a given situation.4 The principle generalizes without remainder. Every actual entity, once it has achieved its satisfaction, belongs to the nature of every subsequent becoming as a potential for it.5
The occasion α issues from occasions that collectively constitute its past, and that past is ingredient in α's own concrescence precisely because those prior occasions have objective immortality — they are there to be prehended, not as living subjects but as completed, determinate facts.6 Even God exemplifies this structure. The primordial nature is never in the past and always in concrescence; but the consequent nature — the physical prehension of derivative actual entities — gives God objective immortality in both natures, and the objective immortality of the consequent nature is what grounds the intuition, common to the great religions, that what has been is somehow preserved and not merely lost.7 So perishing is not the opposite of becoming; it is its condition. How the past perishes is how the future becomes.8
The actual entity terminates its becoming in one complex feeling involving a completely determinate bond with every item in the universe, the bond being either a positive or a negative prehension. This termination is the 'satisfaction' of the actual entity.Process and Reality, pp. 70–71
When they perish, occasions pass from the immediacy of being into the not-being of immediacy. But that does not mean that they are nothing. They remain 'stubborn fact': Pereunt et imputantur.Adventures of Ideas, p. 321
A pure physical prehension is how an occasion in its immediacy of being absorbs another occasion which has passed into the objective immortality of its not-being.Adventures of Ideas, p. 321
It is causation. It is memory. It is perception of derivation. It is emotional conformation to a given situation, an emotional continuity of past with present.Adventures of Ideas, p. 321
It has become a 'being'; and it belongs to the nature of every 'being' that it is a potential for every 'becoming.'Process and Reality, pp. 70–71
Any one occasion α issues from other occasions which collectively form its past. It displays for itself other occasions which collectively form its present.Science and the Modern World, p. 14
God has objective immortality in respect to his primordial nature and his consequent nature. The objective immortality of his consequent nature is considered later (cf. Part V); we are now concerned with his primordial nature.Process and Reality, pp. 58–59
Thus perishing is the initiation of becoming. How the past perishes is how the future becomes.Adventures of Ideas, p. 321