What are its foundational texts — scriptures, books, or writings?

The Qur'an — one identical text across all sects — and the recorded Sunnah of the Prophet ﷺ. Earlier scriptures were true revelations in origin, but only the Qur'an survives as it was revealed.

There is no scripture. The working canon is philosophical: Lucretius' De Rerum Natura, Hume's Dialogues Concerning Natural Religion, d'Holbach's The System of Nature, Darwin's On the Origin of Species, Russell's Why I Am Not a Christian, and recent works such as Dawkins' The God Delusion.

No scripture. The working canon is a shelf of arguments: Hume's Dialogues Concerning Natural Religion (1779), Huxley's essays 'Agnosticism' and 'Agnosticism and Christianity' (1889), Clifford's 'The Ethics of Belief' (1877), Leslie Stephen's 'An Agnostic's Apology' (1876), and Russell's twentieth-century essays.

The Bible: the Old Testament (the Hebrew Scriptures) and the New Testament — 27 books written in Greek: four Gospels, the Acts, twenty-one letters, and Revelation. Catholic and Orthodox Bibles include extra Old Testament books (the deuterocanon) that Protestant Bibles omit.

The Tanakh — Torah (the five books of Moses), Prophets, and Writings, twenty-four books in the traditional count — together with the Oral Torah: Mishnah, Talmud, and midrash. Later pillars include Rashi's commentaries, Maimonides' Mishneh Torah, Karo's Shulchan Arukh, and, for the mystics, the Zohar.

The Tipitaka («three baskets»): the monastic rule (Vinaya), the Buddha's discourses (Suttas), and systematic philosophy (Abhidhamma) — preserved in Pali by the Theravada. The Mahayana adds sutras such as the Lotus and the Heart Sutra; Tibet preserves its own vast canon, the Kangyur and Tengyur.

Two tiers. Shruti ("heard"): the four Vedas — Rig, Sama, Yajur, Atharva — each ending in Upanishads. Smriti ("remembered"): the epics (the Mahabharata with the Bhagavad Gita, and the Ramayana), the Puranas, and law texts such as the Manusmriti; in practice the Gita and the epics shape most Hindus' faith more than the Vedas themselves.

The Guru Granth Sahib — 1,430 standardized pages of hymns by six of the Gurus together with Hindu and Muslim saints, among them Kabir and Shaikh Farid. Beside it stand the Dasam Granth (writings attributed to Guru Gobind Singh, whose status Sikhs debate), the vars of Bhai Gurdas, and the modern code of conduct, the Sikh Rahit Maryada.

No scripture. Its canon is a shelf of arguments and laws: Locke's A Letter Concerning Toleration (1689), Mill's On Liberty (1859), Holyoake's English Secularism (1896), Rawls's Political Liberalism (1993) — and constitutional texts such as the First Amendment (1791) and the French law of 1905.

No scripture. The working canon is the Humanist Manifestos I–III (1933, 1973, 2003) and the Amsterdam Declarations (1952, 2002, 2022), read alongside a shelf of arguments: Dewey’s A Common Faith, Russell, Kurtz, Grayling, Kitcher.

No scripture — an open canon of argument: Locke's Two Treatises and Letter Concerning Toleration, Smith's Wealth of Nations, Mill's On Liberty, Constant, Tocqueville, Berlin, Rawls's A Theory of Justice, and Hayek — plus public founding documents such as the US Bill of Rights, the 1789 Declaration, and the Universal Declaration of Human Rights.

No scripture; a canon of argued books: Wollstonecraft's Vindication (1792), Mill's The Subjection of Women (1869), de Beauvoir's The Second Sex (1949), Friedan's The Feminine Mystique (1963), hooks's Feminism Is for Everybody (2000), and Crenshaw's essays on intersectionality — alongside documents such as the Declaration of Sentiments and CEDAW.

No scripture. Its working canon: Herder on language and Volk, Fichte's Addresses to the German Nation, Mazzini's The Duties of Man, Renan's What Is a Nation?, and Mill's chapter on nationality; alongside them, anthems, declarations of independence, and national histories function as founding texts.