Objection 1. It would seem that fate is not in created things. For Augustine says (De Civ. Dei v, 1) that the "Divine will or power is called fate." But the Divine will or power is not in creatures, but in God. Therefore fate is not in creatures but in God.
Objection 2. Further, fate is compared to things that happen by fate, as their cause; as the very use of the word proves. But the universal cause that of itself effects what takes place by accident here below, is God alone, as stated above (Article 1). Therefore fate is in God, and not in creatures.
Objection 3. Further, if fate is in creatures, it is either a substance or an accident: and whichever it is it must be multiplied according to the number of creatures. Since, therefore, fate seems to be one thing only, it seems that fate is not in creatures, but in God.
On the contrary, Boethius says (De Consol. iv): "Fate is a disposition inherent to changeable things."
I answer that, As is clear from what has been stated above (22, 3; 103, 6), Divine Providence produces effects through mediate causes. We can therefore consider the ordering of the effects in two ways.
Firstly, as being in God Himself: and thus the ordering of the effects is called Providence. But if we consider this ordering as being in the mediate causes ordered by God to the production of certain effects, thus it has the nature of fate. This is what Boethius says (De Consol. iv): "Fate is worked out when Divine Providence is served by certain spirits; whether by the soul, or by all nature itself which obeys Him, whether by the heavenly movements of the stars, whether by the angelic power, or by the ingenuity of the demons, whether by some of these, or by all, the chain of fate is forged." Of each of these things we have spoken above (1; 104, 2; 110, 1; 113; 114). It is therefore manifest that fate is in the created causes themselves, as ordered by God to the production of their effects.
Reply to Objection 1. The ordering itself of second causes, which Augustine (De Civ. Dei v, 8) calls the "series of causes," has not the nature of fate, except as dependent on God. Wherefore the Divine power or will can be called fate, as being the cause of fate. But essentially fate is the very disposition or "series," i.e. order, of second causes.
Reply to Objection 2. Fate has the nature of a cause, just as much as the second causes themselves, the ordering of which is called fate.
Reply to Objection 3. Fate is called a disposition, not that disposition which is a species of quality, but in the sense in which it signifies order, which is not a substance, but a relation. And if this order be considered in relation to its principle, it is one; and thus fate is one. But if it be considered in relation to its effects, or to the mediate causes, this fate is multiple. In this sense the poet wrote: "Thy fate draws thee."
Source: Summa Theologica (New Advent)