Moving on from Blake in Nestor, Stephen thinks of a different model for understanding history, with a different way of relating intellectual possibilities to tyrannically stubborn facts. Aristotle's Metaphysics describes coming-into-being as passage from a state of potentiality (dynamis) to a state of actuality (energeia). Stephen rather loosely reads this argument as implying that, in any moment, there are "infinite possibilities" that might become actual. Only one possibility does become actual, so the others are "ousted."
In the following two sentences, he checks himself. Perhaps other possibilities are not infinite; perhaps, in fact, "only" that which becomes actual ever was possible. This line of thought seems closer to what Aristotle says in the Metaphysics, but it is even more discouraging than thinking of unpleasant actualities "ousting" better ones. It would make history one long deterministic process of unrolling a script that has already been (all but) written.
After an unfortunate interruption caused by the need to speak with his pupils (Stephen is not much of a teacher), he returns to his silent Aristotelian interrogation of history: "It must be a movement, then, an actuality of the possible as possible." The allusion here, Thornton observes, is to Aristotle's Physics 201a10: "The fulfillment [completion or actuality, entelecheia, a near-synonym of energeia] of what exists potentially [dynamis], in so far as it exists potentially, is motion [kinesis]." Similar statements, Thornton notes, can be found at Physics 202a7 and 251a9, and Metaphysics 1065b20 ff.
In Oxen of the Sun Stephen applies this Aristotelian logic to the question of contraception, which the Catholic church forbids: "what of those Godpossibled souls that we nightly impossibilise, which is the sin against the Holy Ghost, Very God, Lord and Giver of Life?"