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‘Who’s afraid of underdetermination?’ (‘Not I’, said the Structural Realist) John Worrall Philosophy, Logic & Scientific Method London School of Economics.

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Presentation on theme: "‘Who’s afraid of underdetermination?’ (‘Not I’, said the Structural Realist) John Worrall Philosophy, Logic & Scientific Method London School of Economics."— Presentation transcript:

1 ‘Who’s afraid of underdetermination?’ (‘Not I’, said the Structural Realist) John Worrall Philosophy, Logic & Scientific Method London School of Economics

2 Part 1: Laudan and Leplin leave things much as they were  2 main theses  1. What they claim: There is no “general guarantee of the possibility of empirically equivalent theories” (449)  1’ What the argument – if successful - would establish: ‘any finding of empirical equivalence is both contextual and defeasible’

3 Part 1: Laudan and Leplin leave things much as they were  2. The empirical equivalence of T and T’ does not entail that the choice between T and T’ is evidentially underdetermined:  “ One of a number of empirically equivalent theories may be uniquely preferable on evidentially probative grounds” (450)  AND as a consequence  “The thesis of underdetermination, at least in so far as it is founded on presumptions about the possibility of empirical equivalence for theories.. stands refuted.” (466)

4 Part 1: Laudan and Leplin leave things much as they were  Argument for thesis 1 (1’) uses 3 premises  (i) VRO: the ‘variability of the range of the observable’  (ii) NAP: the ‘need for auxiliaries in prediction’  (iii) IAA: the ‘instability of auxiliary assumptions’

5 Part 1: Laudan and Leplin leave things much as they were  First note an important ambiguity in the term ‘empirically equivalent’ (and in their definition: “theories are empirically equivalent just in case they have the same class of empirical, viz observational, consequences.” (451)

6 Part 1: Laudan and Leplin leave things much as they were  What (i)-(iii) entail is allegedly that:  T and T’ may be empirically equivalent at one ‘stage of science’ but not at some later stage.  VRO is a ‘mistake’ – but …

7 Part 1: Laudan and Leplin leave things much as they were  Use of auxiliaries just seems sloppy  IF T and T’ are ‘single’ ‘isolated’ theories then  IF Duhem is right  (AND he is!)  THEN T and T’ are automatically empirically equivalent since both have set of empirical consequences = Ø

8 Part 1: Laudan and Leplin leave things much as they were  IF we include all the necessary specific, auxiliary, instrumental assumptions to create two theoretical frameworks F and F’ (built around the ‘core’ T and T’)  THEN problem simply re-arises with F and F’  Of course this tie may be broken later – by addition of a further auxiliary to one or other, but the other can then catch up.  Exactly the Duhem way into underdetermination

9 Part 1: Laudan and Leplin leave things much as they were  So there is a general proof of empirical equivalence  Given any finite set of data D and any rival core theories T and T’ we can always engineer the auxiliaries so that both F and F’ entail D.

10 Part 1: Laudan and Leplin leave things much as they were  So in fact everything rests on thesis 2- viz  2. The empirical equivalence of T and T’ does not entail that the choice between T and T’ is evidentially underdetermined:  “ One of a number of empirically equivalent theories may be uniquely preferable on evidentially probative grounds” (450)

11 Part 1: Laudan and Leplin leave things much as they were  This has to be correct of course  (as those of us who think that there is a solution to the ‘Duhem problem’ have long banged on about)  Prediction/Accommodation

12 Part 1: Laudan and Leplin leave things much as they were  L & L’s own arguments somewhat obfuscatory  A. ‘significant evidential support may be provided for a theory by results that are not empirical consequences of the theory.’ (460)  B. ‘true empirical consequences need lend no evidential support to a theory.’ (ibid)

13 Part 1: Laudan and Leplin leave things much as they were  B just rests on a confusion between ‘no support’ and ‘not much support’  A: argument 1 – ‘next instance’  argument 2 – ‘spread of support’ to rest of a theory  BUT only when theory is unified  My prediction/ accommodation distinction similarly dependent on this sort of judgment  So back to where we always were

14 Part 2: Underdetermination and Structural Realism

15 Underdetermination and Structural Realism  “But these are merely names of the images which we substituted for the real objects which Nature will hide for ever from our eyes. The true relations between these real objects are the only reality we can attain ….”  “If the relations are known to us, what does it matter if we think it convenient to replace one image by another’  In fact anything you said about those ‘images’ would be ‘illusory’/’meaningless’  (Or at best of some heuristic value)

16 Underdetermination and Structural Realism  Hence (E)SR: although our current theories may not be true, their basic theoretical terms may have no real referent – and we cannot, in principle, know whether or not they have -, nonetheless it is reasonable to believe that they are – at least approximately – structurally correct.

17 Underdetermination and Structural Realism  That is, the structure of our successful theories reflects to some extent the real structure of the universe.  And it’s reasonable to believe this, despite scientific “revolutions”, precisely because structure is preserved (or quasi-preserved) through “revolutionary” change.  And of course because each successive theory has enjoyed striking and independent predictive success (NMA)

18 Underdetermination and Structural Realism  SR is clearly committed to the view that the full cognitive content of any theory T is captured by the Ramsey sentence of T  And a good job too!

19 Why the only sensible view is the ‘Ramsey view’  First, what is the RT of any given T?  Ramsey’s whole approach – just like the whole underdetermination issue - is based on making a distinction between theoretical and observational terms.

20 Why the only sensible view is the ‘Ramsey view’  Any scientific theory S will therefore involve a number of theoretical predicates T 1,…, T n and a number of observational predicates O 1,…,O m  So we can write S as S (T 1,…,T n ; O 1,…,O m )

21 Why the only sensible view is the ‘Ramsey view’  Then the Ramsey sentence RT of T is formed by  (i) replacing all occurrences of any theoretical predicate T i by a variable Θ i to form  S (Θ 1,…,Θ n ; O 1,…,O m ); and  (ii) existentially quantifying on all those variables to form:  VΘ 1, …,VΘ n S (Θ 1,…,Θ n ; O 1,…,O m )

22 Why the only sensible view is the ‘Ramsey view’  So why is it obvious that the full cognitive content of any theory T is captured by its RT?  First and foremost: everybody agrees (though then forgets it) that standard referential semantics is entirely misleading  At any rate when it comes to theoretical ‘terms’ in science  You – obviously – can’t stand outside of all theory and compare what the theory says with an independently given reality

23 Why the only sensible view is the ‘Ramsey view’  ‘Global descriptivism’ (at least so far as theoretical terms are concerned)  Causal referential talk would be ‘just more theory’  Unless you appeal to something mystical (clearly unobservable but nonetheless somehow apprehendable ‘semantic glue’)

24 Why the only sensible view is the ‘Ramsey view’  If asked ‘what does ‘gluon’ mean’? I can only rehearse the latest theories involving gluons  N.B. All of those theories  (Lots of mistakes made by leaving some theory ‘outside’ (i.e. unRamseyfied))  That is, a gluon, so far as we can tell, is the whatever it is that does this that and the other (as stated by those theories)  But then if you have accepted this, you have accepted the ‘Ramsey view’

25 Ramseyfication and Underdetermination  Lots of ways of convincing yourself there is a problem with underdetermination that are immediately obviated once you accept Ramsey.  For example:  1. The ‘natural’ argument  2. Tacking paradox  3. Schmelectron theory  4. As if

26 Ramseyfication and Underdetermination  1. The ‘natural’ argument:  Take any theory T and take the set O of the theory’s consequences that are expressible entirely in the observation language  Take any conservative extension of O back into the full language  There are indefinitely many of those  BUT R(T) is itself expressible in the observation language

27 Ramseyfication and Underdetermination  If we restrict initially to the data set, then things are different –  But that takes us back to Duhem and unity

28 Ramseyfication and Underdetermination  2. The Tacking paradox  T’: GTR & God exists has the same set of observational consequences as T: GTR  Moreover so does T’’: GTR & ¬ God exists  T’ and T’’ are mutually inconsistent  You want to say that T’ and T’’ are only nominally different – they have no ‘cognitive content’ not already held by T

29 Ramseyfication and Underdetermination  R(T’) = R(T) & a tautology* = R(T)  R(T’’) = R(T) & a tautology** = R(T)  * VΦVx (Φ x) (take Φ = x=x)  ** V Φ Λx(¬ Φ x) (take Φ = ¬(x=x))

30 Ramseyfication and Underdetermination  Take T:current theory of electrons  T’ says the same except that you consistently substitute ‘schmelectron’ for ‘electron’  R(T) = R(T’)

31 Ramseyfication and Underdetermination  4. T: theory of electrons  T’: Everything is as if electrons (as described by T) exist  Always mystified by this – T’ just a reformulation of T  Just a reexpression of the Ramsey sentence  If you add ‘ but actually they don’t exist’?  Only sense that can be made is surely forward- looking  But this theory of the future will be a different theory with a different Ramsey sentence

32 Ramseyfication and Underdetermination  Summary:  1. The ‘Duhem problem’ can be solved satisfactorily – hence the main way into alleged undetermination is pre-blocked  (Laudan & Leplin only appear to add something to this.)  2. Several of the other ways in which you might think there is a problem of underdetermination evaporate once you take the Ramsey view.

33 The ‘Ramsey view’ and the Newman ‘objection’  Since so many people seem to believe that the result shows that SR collapses into anti- realism, let me start to try to erode that belief:  1. Neither Ketland nor Putnam nor Newman has proved that SR entails that any two ‘empirically equivalent’ theories, in the normal sense, are equally true (or approximately true or, rather, approximately reflect an external reality)

34 The ‘Ramsey view’ and the Newman ‘objection’  2. Not just a question of getting the data right. First the two theories share all the consequences expressible in the observational language  3. And clearly some of these may be theoretical in anyone’s book – e.g. ‘there are unobservables’ (i.e objects with no (directly) observable properties) is (a) purely in the observation language and (b) clearly theoretical.

35 The ‘Ramsey view’ and the Newman ‘objection’  4. Moreover, the theories that SR takes to reflect external reality are not only (predictively) empirically successful but also unified.  (So SR would claim that Copernican theory reflects reality better than Ptolemaic, despite their ‘data’ equivalence (not empirical equivalence), because of the greater unity of Copernican theory.)

36 The ‘Ramsey view’ and the Newman ‘objection’  5. Surely the RT says that the theoretical terms exist – it characterises them in observational terms, or – better - in how they interrelate with one another and how they structure the phenomena – but this is patently not to eliminate them.  (6. Cp Quine’s famous account of ontological commitment)

37 The ‘Ramsey view’ and the Newman ‘objection’  (7. David Lewis ‘My proposal could be called an elimination of theoretical terms, if you must; for to define them is show how to do without them. But it is better called a vindication of theoretical terms; for to define them is to show that there is no good reason to want to do without them.’)

38 Is Structural Realism really realism?  Many will be unconvinced: if this is really the SR that you defend, then for all you say,it isn’t really realism.  Danger of quibbling about words – call it anti- realism if you like  (there certainly are ‘realisms’ that it is anti!)  Doesn’t count on either of Putnam’s definitions  A. A realist needs to assert that a theory T may be false even though its RT is true

39 Is Structural Realism really realism?  B. A realist asserts that the theoretical terms in our current successful theories in mature science refer (though she can then allow that what those theories say about the entities to which they refer is only ‘approximately’ rather than outright true)  (In fact SR asserts that the mode of reference of its terms is just as problematic, uncharacterisable as the approximate truth of a theory T.)

40 Is Structural Realism really realism?  So why do I hold that the right judgement is that SR is a version of realism?  What is realism?  1. “Metaphysical” realism: the assertion of the existence of a reality independent of the human mind???  NO: 1’. There exists a structured reality of which the mind is a part; and, far from imposing their own order on things, our mental operations are simply governed by the fixed laws which describe the workings of Nature.

41 Is Structural Realism really realism?  2. “Methodological realism” = 1’ + the structure of reality is at least in part intelligible to the human mind  3. Scientific realism = 1’ successful theories – the unified theories that explain the phenomena without ad hoc assumptions – are ‘approximately true’.

42 Is Structural Realism really realism?  IF you are wedded to a correspondence or semantic view of truth as your account of corresponding with reality, then SR does not count.  But there is no reason why the way in which a theory mirrors reality should be the usual term-by-term mapping described by traditional semantics

43 Is Structural Realism really realism?  SR takes it that the mathematical structure of a theory may globally reflect reality without each of its components referring (or being known to refer) to a separate item of that reality.  If you insist on reference for truth (or “near reference” for approximate truth) then SR is not realism  BUT there’s no sustainable version of realism attainable if you thus insist

44 Is Structural Realism really realism?  SR takes it that the mathematical structure of a theory may globally reflect reality without each of its components referring to a separate item of that reality.  If you insist on reference for truth (or “near reference” for approximate truth) then SR is not realism  BUT there’s no sustainable version of realism attainable if you thus insist  Structural realism is the only viable position (my confusion, following Poincaré)

45 Is Structural Realism really realism?  Duhem([1906], 28):  The highest test, therefore, of our holding a classification as a natural one is to ask it to indicate in advance things which the future alone will reveal. And when the experiment is made and confirms the predictions obtained from our theory, we feel strengthened in our conviction that the relations established by our reason among abstract notions truly correspond to relations among things.  That’s all it is! Accept it!


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