18 Next to the knowledge of this venerable and glorious and all-holy Faith, learn further what you yourself art: that as man you are of a two-fold nature, consisting of soul and body; and that, as was said a short time ago, the same God is the Creator both of soul and body. Know also that you have a soul self-governed, the noblest work of God, made after the image of its Creator: immortal because of God that gives it immortality; a living being, rational, imperishable, because of Him that bestowed these gifts: having free power to do what it wills. For it is not according to your nativity that you sin, nor is it by the power of chance that you commit fornication, nor, as some idly talk, do the conjunctions of the stars compel you to give yourself to wantonness. Why do you shrink from confessing your own evil deeds, and ascribe the blame to the innocent stars? Give no more heed, pray, to astrologers; for of these the divine Scripture says, Let the stargazers of the heaven stand up and save you, and what follows: Behold, they all shall be consumed as stubble on the fire, and shall not deliver their soul from the flame.
Source: Catechetical Lectures (New Advent)