Below, I have listed the classical authorities in many of the principal disciplines (the liberal arts, the humanities, and the sciences). While it is difficult to define precisely what constitutes a "classic," demarcating a work from other works, which are not "classics," we can say this: All disciplines develop within living traditions. They have a history. A classic is a work that comes somehow causally and chronologically at the beginning of a discipline or some major stage in its historical development. It is, in a way, a universal cause or font for the discipline either as a whole or in one of its principal stages of development. The list below is unavoidably incomplete. View it as a working document.

For a discussion of the nature and importance of the classics, see John Henry Newman, "Christianity and Letters: A Lecture to the School of Philosophy and Letters (November, 1854)."

I. Sciences

A. Speculative Sciences

1. Divine Science / Theology

i. Sacred Theology: 

Principal authority: Sacred Scripture (i.e., the Bible)

Secondary authorities: Pseudo-Dionysius (Corpus Dionysiacum: Divine Names, Mystical Theology, Celstial Hierarchy, Ecclesiastical Hierarchy), Boethius (De Trinitate, Contra Eutychen et Nestorium, Quomodo substantiae [De hebdomadibus], Consolatio philosophiae), Augustine (De Trinitate), Hilary of Poitiers (De Trinitate)

Principal scholastic textbooks: Peter Lombard (Sentences), Thomas Aquinas, OP (Summa theologiae, Catena aurea in quatuor Evangelia)

ii. Metaphysics [i.e., First Philosophy; Natural Theology; Ontology; Wisdom]: Aristotle (Metaphysics), Anonymous (Pseudo-Aristotle) (Liber de causis), Avicenna (Metaphysics of the Healing), Plato (Timaeus), Francisco Suarez, SJ (Disputationes Metaphysicae)

2. Mathematics (see Quadrivium)

3. Natural philosophy [i.e., Natural science]

i. Physics: Aristotle (Physics); Plato (Timaeus)

ii. Chemistry: Aristotle (De generatione et corruptione); Plato (Timaeus)

iii. Psychology: Aristotle (De anima, De sensu et sensato, De memoria et reminiscentia, De somno et vigilia), Avicenna (Liber de anima); Plato (Timaeus)

iv. Biology: Aristotle (De partibus animalium, De historia animalium, De progressu animalium, De motu animalium, De iuventute, De respiratione, De morte, De longitudine et brevitate vitae), Galen (Galenic corpus [misc.]); Plato (Timaeus)

v. Cosmology: Aristotle (De caelo et mundo [NB: This work studies the physical causes of the motion of astronomical bodies]), Ptolemy (Almagest [NB: This work studies astronomical bodies using principles borrowed from mathematical disciplines]); Plato (Timaeus)

B. Morals / Practical Sciences

1. Individual & general ethics: 

   1. Greco-Roman: 

      1. Plato (Gorgias, The Republic)

      2. Aristotle (Nicomachean Ethics, Ethica Eudemia, Magna moralia)

      3. Epicurean: Epicurus (The Letter to Menoeceus)

      4. Stoic: Cicero (De officiis, Tusculanae Disputationes), Seneca (Letters)

   2. Catholic: 

      1. Patristic: Augustine (On Lying, On the Good of Marriage), Pope Gregory the Great (Moralia in Job [6th cent.])

      2. Scholastic: Thomas Aquinas (ST I-II and II-II [13th cent.]), Alphonsus Liguori (Theologia moralis [1748])

   3. Modern:

      1. Hume (A Treatise of Human Nature [1739-1740], An Enquiry Concerning the Principles of Morals [1751])

      2. Deontology: Kant (Groundwork of the Metaphysics of Morals [1785], Critique of Practical Reason [1788])

      3. Utilitarianism: Bentham (An Introduction to the Principles of Morals and Legislation [1789]), John Stuart Mill (Utilitarianism [1861])

   4. Contemporary

      1. Intuitionism: Henry Sidgwick (The Methods of Ethics [1874]), G. E. Moore (Principia Ethica [1903])

      2. Emotivism: A. J. Ayer (Language, Truth and Logic [1936]), C. L. Stevenson (Ethics and Language [1945])

      3. Aristotelian: Alasdair MacIntyre (After Virtue [1981])

2. (Household) economics: Aristotle (Oeconomica)

3. Politics: 

   1. Greco-Roman: Plato (The Republic, Laws), Aristotle (Politics), Cicero (De officiis, De re publica, De legibus), Augustine (De civitate Dei)

   2. Medieval Arabophonic: Alfarabi (On the Perfect State)

   3. Medieval scholastic: John of Salisbury (Politicraticus [12th cent.]), Thomas Aquinas (ST I-II, qq. 90-108; De regno [13th cent.]), Giles of Rome (De regimine principum, De ecclesiastica potestate [13th cent.])

   4. Modern: 

      1. Renaissance: Thomas More (Utopia [1516]), Machiavelli (Discourses on Livy [1531], The Prince [1532])

      2. Scholastic: Francisco Suarez (De legibus ac Deo legislatore [1612], Defensio fidei Catholicae et apostolicae aduersus Anglicanae sectae errores [1613])

      3. Divine Right: Robert Filmer (Patriarcha [mss. 1630s; publ. 1680])

      4. Liberal: Hobbes (Leviathan [1651]), Spinoza (Tractatus Theologico-Politicus [1670]), Locke (Two Treatises on Government [1689], A Letter Concerning Toleration [1689]), Montesquieu (The Spirit of the Laws [1748]), Rousseau (Discourse on the Origin and Basis of Inequality Among Men [1755], The Social Contract [1762]), John Stuart Mill (On Liberty [1859])

      5. American: Hamilton, Madison, and Jay (Federalist Papers [1787-1788]), Alexis de Tocqueville (Democracy in America [1835, 1840])

      6. Conservatism: Burke (Reflections on the Revolution in France [1790]), Kirk (The Conservative Mind [1953])

II. Arts

C. Liberal arts

1. Trivium

i. Grammar: Priscian (Prisciani institutionum grammaticalium librorum I-XVI), Donatus (Ars maior, Ars minor), Aristotle (De interpretatione)

ii. Logic / dialectic: Aristotle (Organon: Categories, De interpretatione, Prior Analytics, Posterior Analytics, Topics, Sophistical Refutations), Porphyry (Isagoge), Boethius (Commentaries on Isagoge, Categories, and De interpretatione; De topicis differentiis; In Ciceronis Topica)

a. 1st operation of intellect (simple understanding): Porphyry (Isagoge), Aristotle (Categories)

b. 2nd operation of intellect (judgment / composition and division): Aristotle (De interpretatione)

c. 3rd operation of intellect (reasoning): Aristotle (Prior Analytics, Posterior Analytics, Topics, Sophistical Refutations), Boethius (De topicis differentis, In Ciceronis Topica)

iii. Rhetoric: Aristotle (On Rhetoric), Cicero (De inventione, Catilinarian Orations), Augustine (De doctrina Christiana)

2. Quadrivium

i. Arithmetic: Euclid (Elements VII-X)

ii. Geometry: Euclid (Elements I-VI)

iii. Astronomy: Ptolemy (Almagest)

iv. Music: Boethius (De Institutione Musica)

I. Humanities

C. Poetry

1. Theory: Aristotle (Poetics) 

2. Exemplars: 

   1. Greek: Homer (Iliad and Odyssey), Hesiod (Theogony, Work and Days)

   2. Latin: Virgil (Aeneid), Ovid (Metamorphoses)

D. History

1. Universal history: Peter Comestor (Historia scolastica), Augustine (De civitate Dei)

2. General Greco-Roman history: Plutarch (Parallel Lives)

3. Greek history

   1. History of the gods: Hesiod (Theogony), Augustine (City of God)

   2. Heroic age: Homer (Iliad and Odyssey)

   3. Persian war: Heroditus (The Histories)

   4. Peloponnesian War: Thucydides (The History of the Peloponnesian War), Xenophon (Hellenica and Anabasis)

   5. Alexander the Great: Arrian (The Campaigns of Alexander)

4.  Roman history

   1. Legendary pre-history of the Roman people going back to Troy: Virgil (Aeneid)

   2. From foundation of Rome through Republic: Livy (History of Rome)

   3. Punic Wars: Polybius (The Histories)

   4. Roman emperors: Tacitus (Annals, Histories), Seutonius (The Twelve Caesars)

5. Ecclesiastical History

   1. Apostolic Age to Constantine: Eusebius of Caesarea (Historia Ecclesiastica, The Life of Constantine)

   2. National histories: 

      1. England: Bede (Ecclesiastical History of the English People)

      2. France: Gregory of Tours (History of the Franks), Einhard (The Life of Charlemagne)

      3. Germany: Tacitus (Germania), Adam Bremen (Gesta Hammaburgensis Ecclesiae Pontificum [History of the Archbishops of Hamburg-Bremen]), Einhard (The Life of Charlemagne)

      4. Ireland: St. Patrick (Confessio)