Period: ~1600–1750 | Context: two major projects for founding secure knowledge — through reason (innate, a priori) or through experience (a posteriori)

The common problem

Both movements answer the question: how are secure knowledge and science possible?

  • Rationalism (Descartes, Spinoza, Leibniz): certain knowledge starts from innate or a priori principles in reason; sensation “hides” the cause — one must “jump over the wall” through pure reason
  • Empiricism (Bacon, Locke, Berkeley, Hume): knowledge begins and is grounded in sensory experience; sensation “reveals” the cause — one must “reach the other side of the wall” by inspecting this side

Kant, in the 18th century, will attempt to synthesize these two positions.

Part I — Rationalism

1. René Descartes (1596–1650) — “Father of Rationalism”

Project: to find the first absolutely certain truths and from them deduce all knowledge — as in mathematics.

The Method (Discourse on Method, 1637)

Four rules:

  1. Evidence: accept only what presents itself clearly and distinctly to reason (no hasty judgment)
  2. Analysis: divide each difficulty into as many parts as possible
  3. Synthesis: conduct thoughts from the simplest and easiest to the most complex
  4. Enumeration: review and verify so as to omit nothing

Before applying it to philosophy, he applies it to mathematics (the only science with certain demonstrations). Provisional morality: obey the laws and customs in force while he seeks definitive truth.

Methodological Doubt (Meditations, 1641)

  • The senses sometimes deceive → he doubts sensory perceptions
  • We sometimes err in reasoning → he doubts rational knowledge
  • He may be dreaming → he doubts all reality
  • Hypothesis of an omnipotent “evil genius” deceiving him → radical doubt of everything

Cogito ergo sum (“I think, therefore I am”): the only certainty that doubt cannot eliminate is that, while I doubt, I am thinking — and thinking presupposes that I exist. It is the first principle of modern philosophy.

Proofs of God’s existence

  1. Causality of ideas: I have the idea of an infinitely perfect being; this idea cannot come from me (an imperfect being) → it came from God
  2. Ontological argument (Cartesian version): God = the supremely perfect being; existing is a perfection → God necessarily exists

God does not deceive → I can trust in reason and the senses (used correctly) → the external world exists

Mind-body dualism

  • Res cogitans (thinking thing): the soul/mind — substance whose attribute is thought
  • Res extensa (extended thing): the body/matter — substance whose attribute is extension
  • Man = union of the two substances (problem: how do they communicate?)
  • Cartesian solution: the pineal gland as point of interaction

Innate ideas

Some ideas do not come from experience: the idea of God, mathematical axioms, the idea of infinity

Works

  • Discourse on Method (1637); Meditations on First Philosophy (1641); Principles of Philosophy (1644); The Passions of the Soul (1649)

2. Nicolas Malebranche (1638–1715)

  • Occasionalism: mind and body do not interact causally; God is the sole real agent; every “cause” is merely an occasion for God’s action
  • Influence of Augustine and Descartes
  • Works: The Search after Truth

3. Benedictus de Spinoza / Baruch Spinoza (1632–1677)

Project: to apply the geometric method to philosophy — definitions, axioms, propositions, demonstrations.

Monism of substance

  • There exists one unique substance: Deus sive Natura (God or Nature)
  • This substance has infinite attributes, of which we know two: thought and extension
  • Individual beings are modes (modifications) of this unique substance

Consequences

  • Pantheism/Immanentism: God is not a transcendent creator — God is nature itself in its totality
  • Absolute determinism: everything that happens is necessary; there is no contingency, nor free will in the usual sense
  • Freedom = understanding necessity; acting according to reason (adequate cause) rather than being moved by external passions
  • Ethics as geometry: passions have necessary causes; knowledge of the third kind (intuition sub specie aeternitatis) liberates

Three kinds of knowledge

  1. Opinion/Imagination: confused images — source of error
  2. Reason: common notions, necessary relations — adequate knowledge
  3. Intuition (scientia intuitiva): knowledge of God and things as parts of the whole; intellectual love of God

Politics

  • Theological-Political Treatise: separation of theology and philosophy; democracy as the best regime for freedom of thought

Works

  • Ethics Demonstrated in Geometrical Order (1677, posthumous); Theological-Political Treatise (1670); Political Treatise

4. Gottfried Wilhelm Leibniz (1646–1716)

Project: complete metaphysical system that reconciles modern science, theology, and traditional philosophy.

Monads

  • Ultimate reality is composed of monads — simple, immaterial substances, without windows (they do not interact causally)
  • Each monad mirrors the entire universe from its own point of view (perceptions)
  • Hierarchy: bare monads → souls (animals) → spirits/minds (humans) → God (Monad of Monads)

Pre-established harmony

  • God, in creating, programmed each monad so that its perceptions coincide with those of all others — like two clocks set together
  • Solution to the mind-body problem without occasionalism or real interaction

Logic and Principles

  • Two great principles: identity/non-contradiction (truths of reason) and sufficient reason (truths of fact — nothing happens without reason)
  • Project of a characteristica universalis — universal formal language of thought (anticipates symbolic logic)

Theodicy

  • God created the best of all possible worlds — the one with the maximum perfection compatible with the existence of evil
  • Evil is privation of being, not a real entity
  • “We live in the best of all possible worlds” — ridiculed by Voltaire in Candide

Co-invention of Infinitesimal Calculus

  • Independently of Newton (1675–1676); Leibniz’s notation (dy/dx, ∫) is what is used today

Works

  • Discourse on Metaphysics (1686); New Essays on Human Understanding (1704, posthumous 1765, against Locke); Theodicy (1710); Monadology (1714)

Part II — Empiricism

1. Francis Bacon (1561–1626) — “Father of Empiricism”

Project: to reform knowledge, replace Aristotelian Organon with a new inductive-experimental method.

The Idols (obstacles to knowledge)

  1. Of the tribe (idola tribus): defects common to the whole human species — tendency toward hasty generalization, interpreting the world according to our desires
  2. Of the cave (idola specus): individual prejudices formed by education, temperament, habits
  3. Of the marketplace/forum (idola fori): deceptions caused by language — words without real referent
  4. Of the theatre (idola theatri): false philosophical doctrines accepted like theatrical spectacles by authority

The New Inductive Method

  • Anticipations of nature (vulgar knowledge) vs. interpretations of nature (scientific knowledge)
  • Method of three tables:
    1. Table of Presence: cases in which the phenomenon occurs
    2. Table of Absence: similar cases in which it does not occur
    3. Table of Degrees: variations in intensity of the phenomenon
  • By elimination of false hypotheses, one arrives at the “first vintage” — provisional hypothesis confirmed by crucial instances (crucial experiments)
  • Science and power coincide: “Knowledge is power”

Works

  • Novum Organum (1620); New Atlantis (scientific utopia, 1627); The Advancement of Learning (1605)

2. John Locke (1632–1704)

Project: to investigate the origin, scope, and limits of human understanding.

Tabula rasa

  • There are no innate ideas (against Descartes); the mind is, at birth, a tabula rasa (blank slate)
  • All knowledge derives from experience: external (sensation) or internal (reflection/introspection)

Primary and secondary qualities

  • Primary (objective): extension, solidity, motion, number, shape — are in the object
  • Secondary (subjective): color, smell, taste, heat — are powers of the object to produce ideas in us

Limits of knowledge

  • We do not know substances in themselves; only their qualities
  • Knowledge is limited to the ideas we have — epistemological humility

Political philosophy (Two Treatises of Government)

  • State of nature is relatively peaceful (different from Hobbes)
  • Inalienable natural rights: life, liberty, and property
  • Government is based on the consent of the governed; if it violates natural rights, the people have the right to revolution
  • Separation of powers: legislative (supreme) and executive/federative

Works

  • Essay Concerning Human Understanding (1690); Two Treatises of Government (1689); Letter Concerning Toleration (1689)

3. George Berkeley (1685–1753)

Project: to refute atheism and materialism by showing that matter without perception is incoherent.

Esse est percipi — “To be is to be perceived”

  • Immaterial material substances independent of perception do not exist
  • Objects exist because they are perceived: by finite minds (us) or by the infinite mind (God)
  • God guarantees the continuity and regularity of the world — the only materialism that Berkeley rejects; the world is “God’s idea”

Works

  • A Treatise Concerning the Principles of Human Knowledge (1710); Three Dialogues between Hylas and Philonous (1713)

4. David Hume (1711–1776)

Empiricism taken to its ultimate consequences — and to the crisis of metaphysics.

Impressions and ideas

  • All mental contents are impressions (vivid perceptions) or ideas (weakened copies of impressions)
  • Principle of copy: every idea derives from a corresponding impression; idea without impression = empty word

Critique of causality

  • We do not perceive necessary connection between causes and effects — only constant conjunction of events
  • Causality is a habit of the mind generated by repetition of conjunction, not a logical or metaphysical necessity
  • Destruction of the foundation of causal metaphysics (including proofs of God’s existence by causality)

The Self as a bundle of perceptions

  • There is no substantial and permanent “I” perceived introspectively
  • The self is a bundle of perceptions (bundle theory) that succeed one another without a persistent substrate

Ethics of moral sentiment

  • Moral judgments are not rational, but expression of sentiments of approval/disapproval
  • Reason is “slave to the passions” — it cannot motivate by itself; it motivates only indirectly, indicating means for desired ends
  • Hume’s guillotine (is-ought gap): one cannot derive an ought from an is (a distinct concept from G. E. Moore’s naturalistic fallacy)

Influence on Kant

  • Hume “awakened Kant from his dogmatic slumber”; Hume’s critique of causality led Kant to revise all metaphysics

Works

  • A Treatise of Human Nature (1739–1740); An Enquiry Concerning Human Understanding (1748); An Enquiry Concerning the Principles of Morals (1751); Dialogues Concerning Natural Religion (1779, posthumous)

General References

  • Reale & Antiseri, History of Philosophy, vol. 3 (Rationalism and Empiricism)
  • Bertrand Russell, History of Western Philosophy, book 3
  • Frederick Copleston, History of Philosophy, vols. 4 and 5
  • Descartes: Meditations (English trans. various); Discourse on Method (various)
  • Spinoza: Ethics (various English trans.)
  • Hume: Enquiry Concerning Human Understanding (various English trans.)
  • Locke: Second Treatise of Government (various English trans.)