I answer that, The disposition of second causes which we call fate, can be considered in two ways: firstly, in regard to the second causes, which are thus disposed or ordered; secondly, in regard to the first principle, namely, God, by Whom they are ordered. Some, therefore, have held that the series itself o[f] dispositions of causes is in itself necessary, so that all things would happen of necessity; for this reason that each effect has a cause, and given a cause the effect must follow of necessity. But this is false, as proved above (Q. 115, A. 6).
Others, on the other hand, held that fate is changeable, even as dependent on Divine Providence. Wherefore the Egyptians said that fate could be changed by certain sacrifices, as Gregory of Nyssa says (Nemesius, De Homine). This too has been disproved above for the reason that it is repugnant to Divine Providence.
We must therefore say that fate, considered in regard to second causes, is changeable; but as subject to Divine Providence, it derives a certain unchangeableness, not of absolute but of conditional necessity. In this sense we say that this conditional is true and necessary: "If God foreknew that this would happen, it will happen." Wherefore Boethius, having said that the chain of fate is fickle, shortly afterwards adds—"which, since it is derived from an unchangeable Providence must also itself be unchangeable."
From this the answers to the objections are clear. _______________________
FOURTH ARTICLE [I, Q. 116, Art. 4]
Whether All Things Are Subject to Fate?
Objection 1: It seems that all things are subject to fate. For Boethius says (De Consol. iv): "The chain of fate moves the heaven and the stars, tempers the elements to one another, and models them by a reciprocal transformation. By fate all things that are born into the world and perish are renewed in a uniform progression of offspring and seed." Nothing therefore seems to be excluded from the domain of fate.
Obj. 2: Further, Augustine says (De Civ. Dei v, 1) that fate is
something real, as referred to the Divine will and power. But the
Divine will is cause of all things that happen, as Augustine says
(De Trin. iii, 1 seqq.). Therefore all things are subject to fate.
Obj. 3: Further, Boethius says (De Consol. iv) that fate "is a disposition inherent to changeable things." But all creatures are changeable, and God alone is truly unchangeable, as stated above (Q. 9, A. 2). Therefore fate is in all things.
On the contrary, Boethius says (De Consol. iv) that "some things subject to Providence are above the ordering of fate."