history 9/17

The Origins of Natural Philosophy

The lecture begins with the "Song of Seikilos," the oldest surviving complete song in history, written by a Greek man named Seikilos in the first century CE.
Background on Ancient Greek Understanding of Nature:
- Between approximately the $7^{th}$ and $5^{th}$ centuries BCE, new ideas emerged regarding how nature works.
- These thinkers, known as "physicoi," engaged in what is termed "natural philosophy" – philosophy about nature and natural phenomena.
- Their work aligns with a definition of science focused on providing accounts of the causes of natural phenomena, explaining why nature operates as it does.

Transition from Divine to Natural Causes

Homer and Hesiod:
- Early Greek texts (e.g., Homer's Iliad, Odyssey; Hesiod's Theogony) attributed natural phenomena to the gods.
- Specific gods held domains of power (e.g., thunderstorms by Zeus, storms by Poseidon).
- The literal belief in these divine causes by the Greek population is largely unanswerable, but it's reasonable to assume gods played a significant role.
The Physicoi's Critical Shift:
- Naturalist philosophers, the physicoi, began to assert that natural phenomena result from other natural processes.
- They attempted to understand nature on its own terms, excluding divine influence.
- This turning point is so critical that most historians of science trace the origins of Western science to this shift, from Homer and Hesiod to thinkers like Thales and Anaximander.
- The core idea: answers to nature's workings lie within nature itself.

Key Questions and Early Physicoi's Responses

Primary Question: What is the world made of?
- Milesian School (Miletus, Anatolia - Western Coast of Turkey):
  - Proponents of monism, specifically material monism – the idea that all diversity of matter ultimately stems from one fundamental substance.
  - Thales: Believed this fundamental substance was water (existing in solid, liquid, or gaseous forms).
  - Anaximander (Thales' student): Proposed the apeiron, a hypothetical, boundless substance, to resolve issues with a water-based universe.
  - Anaximenes (Anaximander's student): Suggested air as the fundamental substance, mediating between Thales' concrete idea and Anaximander's abstraction.
- Empedocles of Agragas:
  - Not a monist; he proposed that the world is composed of four fundamental elements: earth, fire, water, and air.
  - The myriad substances of the world arise from the various permutations of these four elements.
- Leucippus of Miletus and Democritus of Abdera:
  - Moved towards a more abstract direction, suggesting the world is fundamentally composed of atoms – tiny, indivisible units of matter.
- Pythagoras of Samos:
  - After traveling and encountering Babylonian and Egyptian mathematics, he suggested that the cosmos is fundamentally made up not of substances, but of numbers.
  - Numbers (distances, weights, magnitudes) provide meaning and structure to matter.
Shifting Focus: Epistemology and Logic
- Later physicoi began to introspectively interrogate their own minds and methods for learning about nature (epistemology).
- Heraclitus of Ephesus:
  - Suggested logic alone is the proper means for understanding the natural world.
  - He posited that our logic taps into a fundamental cosmic logic called the logos.
  - The logos imparts a law-like character to nature, allowing for the discovery of natural laws.
- Parmenides of Elea and Zeno of Elea (the Eleatics):
  - Emphasized trusting only logic above everything else.
  - Argued that if sensory experience (sight, sound, smell, touch) contradicts logic, logic must prevail, as senses can be deceiving.
  - Advanced logical arguments (e.g., Atalanta's race, dichotomy paradox) suggesting the impossibility of motion or change.

Plato: Synthesis and the Rise of Forms

Biography:
- Born Aristocles of Athens (approx. $428/427$ BCE).
- Nickname "Plato" (meaning "broad") possibly refers to the breadth of his writings, or more compellingly, was given by his wrestling coach due to his physique, as he was a "Jimbo" who loved the gym, like his teacher Socrates.
- Student of Socrates; his execution deeply affected Plato.
- Traveled in Italy, spent time with the Pythagorean cult.
- Around age $40$ (approx. $387$ BCE), founded the Academy in Athens, a school for elite young men.
Epistemology: Supremacy of Logic and Reason:
- Followed Parmenides and Zeno in advocating for reason over sensory experience.
- Allegory of the Cave:
  - A thought experiment to illustrate the unreliability of senses.
  - Chained prisoners in a cave only see shadows on a wall, believing them to be reality.
  - Plato argues that our perceived world might be a more sophisticated illusion, and thus our senses cannot be trusted for true knowledge.
  - Only the rational mind and logic can yield trustworthy knowledge about nature.
Metaphysics: The Theory of Forms and the Demiurge:
- What truly matters for Plato are pure concepts rather than physical things, which he called Forms.
- Forms: Original blueprints, master archetypes from which the world's physical diversity is derived (e.g., the form of a pine tree unites all individual pine trees).
- The Allegory of the Cave also points to the Forms, which exist outside the cave, being more fundamental than our everyday sensory experience.
- The Demiurge: Plato argued the universe was made by a grand designer or craftsman, not a creator in the Abrahamic sense, but one who crafted form out of a formless void.
  - This aligns with Parmenides' idea that "something cannot come from nothing" – the cosmos has always existed, the Demiurge merely gave it structure.
  - The Demiurge is not an active participant in the world's daily events, only the original designer, whose "fingerprints of design" are evident in nature's order.
Plato's Physics: A Synthesis:
- Plato synthesized the ideas of Empedocles, Pythagoras, and Democritus.
- He answered the question "what is the universe fundamentally composed of?" by hybridizing elemental, atomistic, and mathematical concepts.
- Platonic Solids as Atoms:
  - Drawing from geometry, Plato identified five fully symmetrical three-dimensional shapes (Platonic solids) as the most perfect forms.
  - These five solids are the indivisible substances or atoms (from Democritus) and correspond to elements (from Empedocles and Pythagoras).
  - Tetrahedron (pyramid): corresponds to Fire.
  - Cube: corresponds to Earth.
  - Octahedron: corresponds to Air.
  - Icosahedron: corresponds to Water.
  - Dodecahedron (fifth solid): Constitutes a fifth element, not found on Earth, but the element of the heavens (planets and stars), the celestial element.
  - Thus, matter is simultaneously elemental, atomistic, and mathematical, with geometric forms being fundamental to the cosmos.

Aristotle: Empiricism and the Cosmos

Biography:
- Born in Stagira, Northern Greece (approx. $384$ BCE).
- Son of Nicomachus, personal physician to King Amyntas of Macedon.
- Joined Plato's Academy in Athens at age $17$ , quickly becoming Plato's finest student, called "the mind of the school."
- After Plato's death (approx. $347$ BCE), left Athens and tutored Alexander of Macedon (Alexander the Great).
- Returned to Athens around $335$ BCE and founded his own school, the Lyceum.
Epistemology: Primacy of Senses and Deduction:
- Aristotle's central disagreement with Plato: The senses can be trusted and are essential for knowledge.
- Without sensory experience, there would be no ideas or logic.
- Rejection of Forms: The truth lies in concrete individuals, not hidden abstract forms; abstracting makes knowledge less accurate, not more.
- While individual particulars are primary realities, abstraction into categories (e.g., "dog," "tree") is necessary to avoid being overwhelmed and for language/thought.
- Process of Knowledge Generation:
  1. Encounter individuals: Particulars are experienced via the senses.
  2. Store in memory: Individuals are remembered based on experiences.
  3. Sort into categories (Intuition): Memories are compared, and individuals are grouped (e.g., this is a tree, that's a dog).
  4. Reason/Abstract: Logic is applied to these abstractions to form general truths (e.g., the broad category of "trees" has shared features).
- Humans are defined as the "rational animal" because they possess reason beyond mere sensory experience (which animals also have).
- Deduction and Syllogism:
  - The model of rationality for Aristotle is deduction – a rigid logical sequence generating new conclusions from premises.
  - Syllogism: A specific form of deductive reasoning.
  - Famous Example:
    - Premise 1 (from observation/memory): All men are mortal.
    - Premise 2 (from observation/intuition): Socrates is a man.
    - Conclusion (deduction): Therefore, Socrates is mortal.
  - Deductive reasoning moves from general truths (e.g., "All men are mortal") to specific inferences (e.g., "Socrates is mortal"). General truths themselves originate from observation of many specific cases.
- This epistemological break is famously depicted in Raphael's School of Athens ( $1511$ ): Plato's hand points upward to abstract forms, while Aristotle's hand gestures down to the physical world of experience.
Aristotle's Natural Philosophy: Matter, Motion, and the Cosmos:
- Motion and Change:
  - Aristotle directly opposes the Eleatic view: Change is obviously possible because it's observed constantly. Logical arguments against change are flawed, not our senses.
  - Change occurs in two ways:
    1. Natural changes: Result from a thing's inherent nature (its qualities, the class it belongs to).
    2. Forced changes: Occur when something is compelled to change by an external force (e.g., collision).
- Natures and Qualities:
  - Things possess basic qualities (light, heavy, cold, hot) derived from sensory experience, memory, and intuition.
  - Four Fundamental Qualities: Hot, Cold, Wet, Dry.
  - Four Terrestrial Elements (combinations of qualities):
    - Air: Wet and Hot
    - Fire: Dry and Hot
    - Water: Wet and Cold
    - Earth: Dry and Cold
  - Each substance has a default quality or natural state (its nature) to which it tends to return if disturbed (e.g., heated water cools down).
  - All motion and change are results of either forced changes or things seeking their natural places/states (e.g., a thrown stone's upward motion is forced; its falling is natural, seeking Earth's natural place).
- The Cosmos:
  - Eternality: The universe is eternal, always existing (like Plato and Parmenides, based on "nothing from nothing").
  - Geocentric Model: The cosmos is a giant sphere with the Earth at its center, ringed by layers of elements.
  - Natural Places of Elements (concentric rings):
    - Earth (center, heavy)
    - Water (above Earth, heavy)
    - Air (above Water, light)
    - Fire (above Air, light)
  - When in their natural places, elements remain motionless unless forced. When displaced, they move in straight lines towards their appropriate natural place (up or down).
  - Aether (Fifth Element):
    - Planets and stars move in circles, an anomaly for other elements.
    - Aristotle reintroduces Plato's fifth element, Aether, as the substance of the heavens.
    - Aether's natural motion is circular, distinguishing it from terrestrial elements. It is neither light nor heavy, hot nor cold.
    - Aether's natural place is the heavens.
  - Proof of Spherical Earth: Greeks knew the Earth was round from observations like ship masts dipping below the horizon and the curvature of the ocean horizon.
  - Eratosthenes' Calculation (approx. $100$ years after Aristotle):
    - Used geometry to calculate Earth's circumference with remarkable accuracy.
    - Observed that in Syene, Egypt, wells were directly illuminated at noon on the summer solstice (sun $90$ degrees overhead).
    - In Alexandria (where he lived), on the same day, he measured the angle of a pole's shadow at noon.
    - This angle ( $7.2$ degrees) represented $1/50$ of a full circle ( $360$ degrees), the arc between Syene and Alexandria.
    - By multiplying the distance between the two cities by $50$ , he estimated Earth's circumference within a few percentage points.
  - The Prime Mover:
    - To explain why the universe isn't static (everything at rest in its natural place), Aristotle proposed the Prime Mover.
    - This deity provided the original force that set the cosmos into motion, like a chain of dominoes.
    - The Prime Mover is the ultimate cause of motion, preventing eternal stagnation.
Longevity and Significance of Aristotle's Model:
- Aristotle's cosmos, with its concentric rings of five elements and principles of natural motion, lasted over two thousand years in the West.
- Reasons for its endurance:
  1. Simplicity and Explanatory Power: It explained natural phenomena with remarkable simplicity and consistency based on available evidence.
  2. Cohesiveness: Explanations fit together without significant contradictions (few "anomalies" in Thomas Kuhn's sense).
  3. Empirical Basis: Physics and astronomy were derived from sensory experience and observation, making it a powerful natural philosophy in its context, contrasting with prior divine explanations or extreme skepticism of senses.
- This Aristotelian model became the dominant framework that figures like Copernicus and Galileo would challenge and displace during the Scientific Revolution of the $16^{th}$ and $17^{th}$ centuries.