From the Catholic Encyclopedia:
Free Will-
Catholic Doctrine …The teaching of St. Augustine is developed by
St. Thomas Aquinas both in theology and philosophy.
Will is rational appetite. Man necessarily desires beatitude, but he can freely choose between different forms of it. Free will is simply this elective power.
Infinite Good is not visible to the intellect in this life.
There are always some drawbacks and deficiencies in every good presented to us. None of them exhausts our intellectual capacity of conceiving the good. Consequently, in deliberate volition, not one of them completely satiates or irresistibly entices the will. In this capability of the intellect for conceiving the universal lies the root of our freedom.
But
God possesses an
infallible knowledge of man’s future actions. How is this prevision possible, if man’s future acts are not necessary?
God does not exist in time. The future and the past are alike ever present to the eternal mind as a man gazing down from a lofty mountain takes in at one momentary glance all the objects which can be apprehended only through a lengthy series of successive experiences by travellers along the winding road beneath, in somewhat similar fashion the intuitive
vision of God apprehends simultaneously what is future to us with all it contains.
Further,
God’s omnipotent providence exercises a complete and perfect control over all events that happen, or will happen, in the universe.
newadvent.org/cathen/06259a.htm#chr