Modern Western Philosophy

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Modern Western Philosophy runs from the early 17th century (Descartes' Meditations, 1641) through the 20th century. It is conventionally divided into:

Rationalism (Descartes, Spinoza, Leibniz) — emphasising reason as source of knowledge.
Empiricism (Locke, Berkeley, Hume) — knowledge from sense experience.
Kant's critical synthesis — Critique of Pure Reason (1781).
German Idealism (Fichte, Schelling, Hegel).
19th-century post-Hegelianism (Marx, Kierkegaard, Nietzsche).
20th-century analytic (Frege, Russell, Wittgenstein, Quine) and continental (Husserl, Heidegger, Sartre, Foucault).

Modern Philosophy

Begins with René Descartes (1596–1650), whose Cogito ergo sum ('I think, therefore I am') marked a turn from medieval authority to autonomous reason. The 'modern' label distinguishes this period from ancient and medieval, and from contemporary postmodern thought after c. 1960.

Rationalism

René Descartes (1596–1650, France)

Father of modern philosophy. Major works: Discourse on Method (1637), Meditations on First Philosophy (1641), Principles of Philosophy (1644).

Methodic doubt — doubt everything to find indubitable foundation.
Cogito ergo sum — "I think, therefore I am" (Meditation II).
Mind-body dualism — res cogitans (thinking substance) and res extensa (extended substance).
Innate ideas — God, mathematics, self.
Cartesian coordinates — co-founder of analytic geometry.

Baruch Spinoza (1632–1677, Netherlands)

Dutch-Jewish philosopher excommunicated from Amsterdam synagogue (1656). Major work: Ethics (published posthumously, 1677).

One substance — Deus sive Natura (God or Nature) — pantheism.
Two known attributes: thought and extension.
Modes: finite individuals are modifications of substance.
Determinism and freedom as understanding necessity.
Geometric method — propositions, demonstrations, scholia.

Gottfried Wilhelm Leibniz (1646–1716, Germany)

Co-inventor of calculus (with Newton). Major works: Discourse on Metaphysics (1686), Monadology (1714), Theodicy (1710).

Monads — simple, indivisible, immaterial substances; "windowless".
Pre-established harmony — God coordinates all monads.
Principle of sufficient reason — nothing happens without a reason.
Best of all possible worlds — God's choice (satirised by Voltaire in Candide).
Symbolic logic — universal characteristic.

Empiricism

John Locke (1632–1704, England)

Major works: Essay Concerning Human Understanding (1689), Two Treatises of Government (1689), Letter Concerning Toleration (1689).

Tabula rasa — the mind at birth is a blank slate; knowledge derives from experience (sensation + reflection).
Primary and secondary qualities — primary (size, shape) inhere in objects; secondary (colour, taste) depend on perceiver.
Natural rights — life, liberty, property; influenced US Declaration of Independence (1776).
Social contract with consent and right of revolution.

George Berkeley (1685–1753, Ireland)

Major work: A Treatise Concerning the Principles of Human Knowledge (1710).

Esse est percipi — "to be is to be perceived".
Immaterialism / subjective idealism — only minds and ideas exist.
God as the perpetual perceiver sustaining reality.

David Hume (1711–1776, Scotland)

Major works: A Treatise of Human Nature (1739–40), An Enquiry Concerning Human Understanding (1748), Dialogues Concerning Natural Religion (posth. 1779).

Impressions and ideas — all ideas derive from prior impressions.
Problem of induction — causation is psychological habit, not logical necessity.
Is-ought problem (Hume's Guillotine) — moral conclusions cannot be derived from factual premises.
Bundle theory of self — no enduring "I", only a bundle of perceptions.
Religious scepticism — critique of miracles and design argument.

Key Points

Rationalism vs. empiricism: source of knowledge — reason or experience.
Hume's challenge woke Kant from his 'dogmatic slumber' (Kant's own words in Prolegomena).
Kant's critical philosophy synthesises rationalism and empiricism while limiting metaphysical claims.
Hegel's dialectic of thesis-antithesis-synthesis is a popular but simplified summary; Hegel preferred 'speculative' to 'dialectical'.

Kant and German Idealism

Immanuel Kant (1724–1804, Königsberg, Prussia)

The most influential modern philosopher. Major works: Critique of Pure Reason (1781, 2nd ed. 1787), Critique of Practical Reason (1788), Critique of Judgment (1790), Groundwork of the Metaphysics of Morals (1785).

Key doctrines:

Transcendental idealism — we know phenomena (appearances), not noumena (things-in-themselves).
Synthetic a priori judgments — geometry, arithmetic, causality.
Twelve categories of understanding; space and time as forms of intuition.
Categorical imperative — "act only on that maxim whereby you can at the same time will that it become a universal law".
Persons as ends in themselves, never merely means.
Perpetual peace — Zum ewigen Frieden (1795).

Georg Wilhelm Friedrich Hegel (1770–1831, Germany)

Major works: Phenomenology of Spirit (1807), Science of Logic (1812–16), Philosophy of Right (1821).

Geist (Spirit) — Absolute Mind unfolding through history.
Dialectic — concepts develop through contradiction and resolution.
History as rational — World Spirit progressing toward freedom.
State as the highest expression of ethical life (Sittlichkeit).

19th-century revolts

Karl Marx (1818–1883, Germany)

Major works: Communist Manifesto (1848, with Engels), Das Kapital (vol. I 1867), Theses on Feuerbach (1845).

Historical materialism — economic base determines superstructure.
Class struggle as engine of history.
Alienation of labour under capitalism.
Communism — abolition of private property.

Søren Kierkegaard (1813–1855, Denmark)

Father of existentialism. Major works: Either/Or (1843), Fear and Trembling (1843), Concluding Unscientific Postscript (1846).

Stages of life — aesthetic, ethical, religious.
Leap of faith — religious commitment beyond reason.
Subjectivity is truth — emphasis on individual existence.

Friedrich Nietzsche (1844–1900, Germany)

Major works: Thus Spoke Zarathustra (1883–85), Beyond Good and Evil (1886), On the Genealogy of Morality (1887).

Will to power as fundamental drive.
Death of God — The Gay Science §125 (1882).
Übermensch (Superman/Overman).
Master and slave morality — critique of Christian ethics.
Eternal recurrence thought experiment.

20th-century philosophy

Analytic tradition

Gottlob Frege (1848–1925) — Begriffsschrift (1879); founder of modern logic; Sinn und Bedeutung.
Bertrand Russell (1872–1970) — Principia Mathematica (1910–13, with Whitehead); theory of descriptions.
Ludwig Wittgenstein (1889–1951) — Tractatus (1921), Philosophical Investigations (1953, posth.); language games.
A.J. Ayer (1910–1989) — Language, Truth and Logic (1936); logical positivism.
W.V.O. Quine (1908–2000) — Two Dogmas of Empiricism (1951); naturalised epistemology.
John Rawls (1921–2002) — A Theory of Justice (1971); veil of ignorance.

Continental tradition

Edmund Husserl (1859–1938) — Logical Investigations (1900–01); phenomenology.
Martin Heidegger (1889–1976) — Being and Time (1927); Dasein, being-in-the-world.
Jean-Paul Sartre (1905–1980) — Being and Nothingness (1943); "existence precedes essence".
Simone de Beauvoir (1908–1986) — The Second Sex (1949); feminist philosophy.
Michel Foucault (1926–1984) — Discipline and Punish (1975); power-knowledge.
Jürgen Habermas (b. 1929) — The Theory of Communicative Action (1981).

For CSS, organise your answer around the four pillars of modern philosophy: (i) rationalism — Descartes (Cogito 1641), Spinoza (Ethics 1677), Leibniz (Monadology 1714); (ii) empiricism — Locke (1689), Berkeley (1710), Hume (1748); (iii) Kant (Critique of Pure Reason 1781); (iv) post-Kantian — Hegel (Phenomenology 1807), Marx (Capital 1867), Nietzsche (Zarathustra 1883). For each thinker: one work + one signature thesis.

Themes across modern philosophy

Epistemology: how do we know? Reason (rationalism) or experience (empiricism)?
Metaphysics: what exists? Substance (Descartes), monism (Spinoza), monads (Leibniz), things-in-themselves (Kant), Spirit (Hegel).
Ethics: how should we live? Duty (Kant), utility (Bentham, Mill), virtue (revived by MacIntyre 1981), authenticity (Sartre).
Political philosophy: from social contract (Locke, Rousseau) through Marx, Mill, Rawls.
Philosophy of mind: from dualism (Descartes) through materialism, functionalism, qualia debates.
Philosophy of language: from Frege's sense/reference through Wittgenstein's language games to Kripkean rigid designators.

Modern philosophy is the indispensable backdrop for understanding contemporary Western thought across science, politics, ethics and aesthetics.