Libertas §3

³ It is with moral liberty, whether in individuals or in communities, that We proceed at once to deal. But, first of all, it will be well to speak briefly of natural liberty; for, though it is distinct and separate from moral liberty, natural freedom is the fountainhead from which liberty of whatsoever kind flows, sua vi suaque sponte . The unanimous consent and judgment of men, which is the trusty voice of nature, recognizes this natural liberty in those only who are endowed with intelligence or reason; and it is by his use of this that man is rightly regarded as responsible for his actions. For, while other animate creatures follow their senses, seeking good and avoiding evil only by instinct, man has reason to guide him in each and every act of his life. Reason sees that whatever things that are held to be good upon earth may exist or may not, and discerning that none of them are of necessity for us, it leaves the will free to choose what it pleases. But man can judge of this contingency, as We say, only because he has a soul that is simple, spiritual, and intellectual - a soul, therefore, which is not produced by matter, and does not depend on matter for its existence; but which is created immediately by God, and, far surpassing the condition of things material, has a life and action of its own so that, knowing the unchangeable and necessary reasons of what is true and good, it sees that no particular kind of good is necessary to us. When, therefore, it is established that man's soul is immortal and endowed with reason and not bound up with things material, the foundation of natural liberty is at once most firmly laid.