Theory and the World

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

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

Unobservables My car battery goes flat if lights are left on

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? …

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

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

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

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

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.

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

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

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

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

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

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, … ?

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.

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

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?

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

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

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

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

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