Now, against the sacrilegious and impious darings of reason, we assert both that God knows all things before they come to pass, and that we do by our free will whatsoever we know and feel to be done by us only because we will it. But that all things come to pass by fate, we do not say; nay we affirm that nothing comes to pass by fate; for we demonstrate that the name of fate, as it is wont to be used by those who speak of fate, meaning thereby the position of the stars at the time of each one’s conception or birth, is an unmeaning word, for astrology itself is a delusion. But an order of causes in which the highest efficiency is attributed to the will of God, we neither deny nor do we designate it by the name of fate, unless, perhaps, we may understand fate to mean that which is spoken, deriving it from fari , to speak; for we cannot deny that it is written in the sacred Scriptures, God has spoken once; these two things have I heard, that power belongs unto God. Also unto You, O God, belongs mercy: for You will render unto every man according to his works. Now the expression, Once has He spoken, is to be understood as meaning immovably , that is, unchangeably has He spoken, inasmuch as He knows unchangeably all things which shall be, and all things which He will do. We might, then, use the word fate in the sense it bears when derived from fari , to speak, had it not already come to be understood in another sense, into which I am unwilling that the hearts of men should unconsciously slide. But it does not follow that, though there is for God a certain order of all causes, there must therefore be nothing depending on the free exercise of our own wills, for our wills themselves are included in that order of causes which is certain to God, and is embraced by His foreknowledge, for human wills are also causes of human actions; and He who foreknew all the causes of things would certainly among those causes not have been ignorant of our wills.
City of God (Book V)
Chapter 9.— Concerning the Foreknowledge of God and the Free Will of Man, in Opposition to the Definition of Cicero.