One of the most important encyclicals we need to rediscover is Pope Leo XIII's Libertas (1888), on the true nature of human liberty. This encyclical explains what true liberty consists of, followed by a lengthy exposition of the Church's condemnation of liberalism, in the Enlightenment/classical sense rather than today's narrower use of the word. Most people who call themselves conservative now would, in certain ways, fall into the category of liberalism as defined by Leo.
Prophetically warning of the evil consequences of political liberalism, Leo also takes aim at various false liberties in which modern people take such pride: freedom of speech, writing, thought, and worship. In each of these instances, liberals fail to recognize that freedom is not the right to do and say what one wants, but to do justice and to speak truth. As starting as Leo's teaching may be to modern Catholics, his fundamental principle is the one that Pope St. John Paul II enunciated when he said that "freedom consists not in doing what we like, but in having the right to do what we ought."
Pope Leo XIII: "Man, by a necessity of his nature, is wholly subject to the most faithful and ever-enduring power of God; and that, as a consequence, any liberty, except that which consists in submission to God and in subjection to His will, is unintelligible. To deny the existence of this authority in God, or to refuse to submit to it, means to act, not as a free man, but as one who treasonably abuses his liberty; and in such a disposition of mind the chief and deadly vice of liberalism essentially consists.
Pope Leo XIII, Libertas https://www.vatican.va/content/leo-xiii/en/encyclicals/documents/hf_l-xiii_enc_20061888_libertas.html
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