According to the Catechism: “In Catholic Doctrine there is a hierarchy of truths, since they vary in their relation to the foundation of the Christian faith.” (#90) The mystery of the Most Holy Trinity is the most fundamental and essential Teaching in the ‘hierarchy of the truths of faith.’ (#234)
There are five foundational truths:
The Blessed Trinity: God is an eternal loving communion of Father, Son, and Holy Spirit
The Person of Jesus: A divine person who took on human nature in the Incarnation
The Paschal Mystery: the suffering, death, resurrection, and ascension of Jesus Christ
The Dignity of the Human Person: made in the image and likeness of God
The Church: the Body of Christ brought to life in the Holy Spirit
Divinely Revealed Truth (Dogma): This is Doctrine that is definitively (meaning that it has been defined) taught by the Church as revealed. It includes all Dogmas, either defined by the Pope (ex-cathedra) or by a Council. These Truths require belief and response by all Catholics. If they don’t, they are in "heresy".
Examples: The articles of the Creed, the Christological dogmas, the Marian dogmas, Christ’s institution of the Sacraments and their efficacy to impart grace, the Real Presence, the sacrificial nature of the Mass, the divine foundation of the Church, the primacy and infallibility of the Roman Pontiff, the existence of original sin, the immortality of the human soul, the immediate recompense after death, the inerrancy of Holy Scripture, the grave immorality of murder.
Non-Revealed, yet Definitive Truth (secondary truths): These are Doctrines that are proposed as infallible because they are matters of faith and morals. They are not revealed in themselves, but they are definitively proposed statements on matters closely connected with revealed truth, and are required to explain them or define them effectively. These Truths require “firm and definitive assent”, ie. All Catholics must accept these Teachings as True. If they don’t, they are in “error”.
Examples: Principle of natural law, seven Sacraments, condemnation of all terms of discrimination, human dignity and equality, human rights, immortality of the human person, the illicitness of prostitution, male-only priesthood, the legitimacy of the election of a pope, the celebration of an ecumenical council, the canonizations of saints.
Authoritative but reformable teaching: These are non-definitive teachings. They are doctrines that help to understand revelation better. They are also called “authentic, but non-infallible teaching.” These doctrines require respect and obedience of will and intellect by all Catholics. If not, they are in “dissent.”
Examples: Biblical criticism, preferential option for the poor, formula for Sacraments, religious liberty, ecumenism, rejection of torture, Anglican orders, teaching on the use of artificial birth control, cremation, capital punishment.
Discipline: These are NOT Doctrine. They are universal laws of the Church. It may include particular laws of a diocese, liturgical norms or Church practice. They require obedience by all Catholics. If not, they are in a state of "disobedience".
Examples: Fasting rules, feasts of obligation, celibate priesthood, directives from curia on religious life, use of art/architecture, First Confession before First Communion.