Liberty, nature’s most exalted gift, the endowment of intellectual and rational beings only, confers on man the dignity of abiding “in the hand of his counsel,” of having power over his own actions. But the manner in which this dignity is exercised is of the greatest moment, inasmuch as on the use made of liberty the highest good and the greatest evil alike depend. Man, indeed, is free to obey his reason, to seek moral good, and to strive unswervingly after his last end. Yet he is free also to turn aside to all other things, and, in pursuing the empty semblance of good, to disturb rightful order and to fall headlong into the destruction which he has voluntarily chosen.
The Redeemer of mankind, Jesus Christ, after restoring and exalting the original dignity of nature, vouchsafed special assistance to the will of man. By the gifts of His grace here, and the promise of heavenly bliss hereafter, He raised it to a nobler state. In like manner this great gift of nature has ever been, and always will be, deservingly cherished by the Catholic Church; for to her alone has been committed the charge of handing down to all ages the benefits purchased for us by Jesus Christ. Yet there are many who imagine that the Church is hostile to human liberty. With a false and absurd notion as to what liberty is, they either pervert the very idea of freedom, or they extend it at their pleasure to many things in respect of which man cannot rightly be regarded as free.
On other occasions, and especially in Our Encyclical Letter Immortale Dei, while treating of the so-called modern liberties, we distinguished between their good and evil elements. We have shown that whatsoever is good in those liberties is as ancient as truth itself, and that the Church has always most willingly approved and practised that good. But whatsoever has been added as new is, to tell the plain truth, of a vitiated nature, the fruit of the disorders of the age and of an insatiate longing after novelties. Seeing, however, that many cling so obstinately to their own opinion in this matter as to imagine these modern liberties, cankered as they are, to be the greatest glory of our age and the very basis of civil life, without which no perfect government can be conceived, We feel it a pressing duty, for the sake of the common good, to treat separately of this subject.
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 distinct and separate from moral liberty, natural freedom is the fountain-head from which liberty of whatsoever kind flows, by its own force and of its own accord. The unanimous consent and judgement of men, which is the trusty voice of nature, recognizes this natural liberty in those only who are endowed with intelligence or reason; and by his use of this, 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 his reason to guide him in each and every act of his life. Reason sees that whatever things are held to be good upon earth, may exist or may not. 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. Far surpassing the condition of things material, it 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.
[From Libertas Humana promulgated 20 June 1888 by His Holiness Pope Leo XIII]
*As an aside, the final paragraph could be interpreted in a way that seems out of keeping with the Thomistic-Aristotelian tradition. Consequently, as a caveat, it should be kept in mind that particular material things are unnecessary, but, barring Divine Intervention of an incomprehensible sort, material reality itself is necessary for man–hence man being created as a being that is unified in body and spirit, their division being an unnatural consequence of original sin.