1. Theory and the World

2. Explanations and Theories
Explanations involve general statements
They allow us to understand why certain things happen and others don’t
Theories are organized systems of such general statements
Theories produce explanations and support our claims to understanding

3. Unobservables Theories so far have been pretty trivial
The statue is brown
The billiard ball is moving
They have all been theories involving observable things
We can directly check whether the things they say exist really do exist
Some theories assume things we can’t see

4. Unobservables
My car battery goes flat if lights are left on

5. Unobservables My car battery goes flat if lights are left on
The explanation for this talks about electrons
We cannot see electrons
What attitude should we take to such claims?
There really are electrons
They are convenient fictions
They are a pretty story – and who cares about the truth? …

6. Instrumentalism
Theories aren’t descriptions they are tools for prediction
The idea that we should take theories to be true is contradicted by experience
We thought light was waves in a medium
The medium was ether
Michelson-Morley showed that ether doesn’t exist
That theory gave a wrong description

7. Instrumentalism
Theories aren’t descriptions they are tools for prediction
The idea that we should take theories to be true is contradicted by experience
We thought illness was caused by an imbalance of humours
The humours were blood, bile, black bile, and phlegm
They don’t exist as humours
That theory gave a wrong description

8. Instrumentalism
Theories aren’t descriptions they are tools for prediction
The idea that we should take theories to be true is contradicted by experience
We thought the Sun went round the Earth
The sun and planets had to be fixed to crystalline spheres
Galileo Galilei showed those spheres don’t exist
That theory gave a wrong description

9. Instrumentalism Make a pessimistic induction
Etheric theory was our best theory, but the things it described didn’t exist
Humoral theory was our best theory, but the things it described didn’t exist
Ptolemaic theory was our best theory, but the things it described didn’t exist …
The things that our best theories describe don’t exist

10. Instrumentalism
The idea that good theories are useful and predictive is confirmed by experience
The wave theory of light allowed progress in optics, explaining interference, refraction, reflection, etc.
The humoural theory explained how purging was beneficial, poisoning was harmful, etc.
The Ptolemaic theory allowed predictions of eclipses, planetary motions, etc.

11. Instrumentalism Make an induction to instrumentalism
Etheric theory was valuable as a predictive tool
Humoral theory was valuable as a predictive tool
Ptolemaic theory was valuable as a predictive tool …
Our best theories are valuable as predictive tools

12. Instrumentalism Make an induction to instrumentalism
Supported by two further observations
We actually do call a theory ‘good’ if it works well as an instrument
We really only reject a theory when it has shown itself to be an ineffective instrument

13. Instrumentalism
Even though pessimism is justifiable, I. seems unsatisfactory
Theories are supposed to be explanations
Explanations tells us ‘why’ and ‘how’ and so on
I. doesn’t tell us anything
I. seems to make explanations impossible in principle
How could the world be inexplicable?
If it is explicable then why not (with all appropriate caution) accept our best theories
To accept them is to believe their world picture

14. Instrumentalism
Instrumentalist may deny that science really needs explanations
Science only needs to give predictions/descriptions of how the world will seem to behave
‘Frontier’ scientists are still scientists, aren’t they?
‘Frontier’ science is a special case
Aristotle accepted undemonstrated truths
But episteme/science included the far larger body of demonstrated truths

15. Realism
An Inference to Best Explanation seems to support Realism about scientific theories
The appropriate IBE isn’t trying to demonstrate the truth of any particular theory
It demonstrates the most rational approach to interpreting any theory

16. Realism
An Inference to Best Explanation seems to support Realism about scientific theories
The pursuit of scientific knowledge shows the following characteristics: A, B, C, …
The following interpretations of scientific theories make sense of those characteristics:
1. Instrumentalism
2. Realism
Interpretation 2 seems to make the best sense, so you conclude
Realism is right
So what play the role of A, B, C, … ?

17. Realism
A: No Miracles
Science is amazingly successful
We rely upon what it predicts in engineering, medicine, etc.
Its success is explicable if it tells us how things really are; otherwise it seems a miracle
The instrumentalist can say Science is successful because it selects the successful theories
But why are they successful? That’s the question.

18. Realism B: Corroborations
Unobservables can be ‘verified’ from several directions
Germs via epidemiology
Germs via electron microscopy
This can be explained if unobservables really exist
There are germs

19. Realism C: Unification
Science aims to unify different fields using theories that replace several unconnected theories
Genetics + chemistry
Electricity + magnetism
They aim at a GUT to unify everything
This makes sense if there is a unified reality that can be described
Does it make sense to try to unify all your tools?

20. Underdeterminism
Instrumentalists also claim that there is never definite support for any particular interpretation of a theory
If we can’t judge between different interpretations then we can’t judge between different claimed sets of unobservables
To take a Realist view is therefore unjustified

21. Underdeterminism Duhem/Quine Hypothesis: The world is flat
Deduction: If it’s flat then ships sailing away will become vanishingly small, but will remain visible
Observational test: Such ships disappear over the horizon.
Conclude?
World is curved
Light bends

22. Underdeterminism Duhem/Quine
It is always possible to defend any theory against all possible observations

23. Underdeterminism Poincaré Theory 1 says that Earth goes around the sun
Theory 2 says that Earth goes around the sun and that everything in the universe is moving at 1000 km/s in the same direction
There are no observations that will allow you to judge between these theories

24. Underdeterminism Poincaré
For any observations there are an infinite number of observationally indistinguishable theories