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General Philosophy · Lecture 8 of 33 · 7:58

2.4 Isaac Newton and Instrumentalism

2.4 Isaac Newton and Instrumentalism on YouTube

Study guide

What this lecture covers

This lecture explains how Isaac Newton built on Kepler, Galileo, Descartes and Boyle to produce a theory of gravity that explained planetary motion with unprecedented simplicity and accuracy. It then examines the philosophical controversy this caused and Newton's own response to it.

Newton showed mathematically that a single force, proportional to each body's mass and inversely proportional to the square of the distance between them, produces exactly the elliptical orbits Kepler had observed, and that the same law explains falling objects on Earth. This discredited Descartes's vortex theory, which Newton proved could not generate elliptical motion. But gravity's action at a distance seemed to violate the mechanistic ideal that had discredited Aristotle, since it required no contact between bodies, and Newton refused to speculate about its underlying cause.

Key ideas

  • Newton's law of gravity: force is proportional to the product of the two masses and inversely proportional to the square of the distance between them.
  • Unifying terrestrial and celestial motion: the same equations explain both the orbits of planets and the fall of objects like cannonballs on Earth.
  • Refutation of vortices: Newton showed mathematically that vortices cannot produce elliptical orbits, discrediting Descartes's physics, though it lingered longer in France than in Britain.
  • The problem of action at a distance: gravity acting between bodies with no contact seemed to violate the mechanical ideal that had replaced Aristotelian 'striving'.
  • 'Hypotheses non fingo': Newton's famous refusal to speculate about the cause of gravity, stating only that his equations matched observation.
  • Instrumentalism: the view that a scientific theory only needs to deliver correct predictions, regardless of whether its underlying entities are real.

Before you watch

  • Watch lectures 2.2 and 2.3 for Descartes's vortex theory and Boyle's corpuscularianism, and note Kepler's discovery of elliptical orbits from lecture 2.3.

Check your understanding

  1. How does Newton's single law of gravity explain both planetary orbits and falling objects on Earth?
  2. Why did Newton's theory of gravity trouble people committed to the mechanical philosophy?
  3. What does 'hypotheses non fingo' mean, and what does it reveal about Newton's attitude to explanation?
  4. How does instrumentalism differ from a view that insists a scientific theory's entities must be real?

Vocabulary

law of gravity (noun)
Newton's rule describing the force of attraction between any two masses.
Newton's law of gravity explains why planets stay in orbit.
proportional (adjective)
Changing at the same rate as another quantity, so their ratio stays constant.
The force is proportional to the product of the two masses.
inversely proportional (phrase)
Decreasing as another quantity increases, in a fixed mathematical relationship.
Gravity is inversely proportional to the square of the distance.
unify (verb)
To bring separate things together under one single explanation.
Newton's law unifies terrestrial and celestial motion.
celestial (adjective)
Relating to the sky or outer space.
The same equations explain celestial and earthly motion.
refutation (noun)
A proof or demonstration that something is false.
Newton's mathematics provided a refutation of vortex theory.
action at a distance (phrase)
The idea that one object can affect another without any physical contact between them.
Gravity's action at a distance troubled mechanistic philosophers.
speculate (verb)
To form a guess or theory without firm evidence.
Newton refused to speculate about the cause of gravity.
hypotheses non fingo (phrase)
Newton's Latin phrase meaning 'I do not make up hypotheses,' referring to unproven causes.
Hypotheses non fingo expresses Newton's refusal to guess at gravity's cause.
instrumentalism (noun)
The view that a scientific theory is valuable for making correct predictions, regardless of whether it describes real underlying entities.
Instrumentalism says a theory just needs to work, not explain reality.
entity (noun)
A thing that exists, especially one referred to in a theory.
Instrumentalism doesn't require a theory's entities to be real.
discredit (verb)
To damage the reputation or credibility of an idea.
Newton's proof discredited Descartes's vortex theory.
linger (verb)
To continue to exist or be believed for longer than expected.
Vortex theory lingered longer in France than in Britain.
unprecedented (adjective)
Never having happened or existed before.
Newton's theory had unprecedented simplicity and accuracy.
build on (phrasal verb)
To use earlier work as a foundation for new work.
Newton built on Kepler, Galileo and Descartes.
controversy (noun)
A public disagreement or dispute about an issue.
Gravity caused philosophical controversy.
mathematically (adverb)
Using the methods and reasoning of mathematics.
Newton showed mathematically that vortices fail.
ideal (mechanistic) (noun)
A standard or principle considered the best or most correct.
Action at a distance violated the mechanistic ideal.
attitude (to explanation) (noun)
A way of thinking about or approaching something.
Hypotheses non fingo reveals Newton's attitude to explanation.
trouble (someone) (verb)
To cause worry or concern for a person or group.
Gravity's action at a distance troubled mechanistic philosophers.

Chapters

From the YouTube description

A series of lectures delivered by Peter Millican to first-year philosophy students at the University of Oxford. The lectures comprise the 8-week General Philosophy course and were delivered in late 2009.

Slides for all his lectures can be found here:
http://podcasts.ox.ac.uk/people/peter-millican

Learn more about Oxford:
http://www.ox.ac.uk

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