I. Scientific Realism: Introduction

Transcription

1 I. Scientific Realism: Introduction 1. Two kinds of realism a) Theory realism: scientific theories provide (or aim to provide) true descriptions (and explanations). b) Entity realism: entities postulated by scientific theories really exist. 2. Some arguments for anti-realism a) Empiricism requires anti-realism: parsimony argument. Empiricism: All knowledge of matters of fact rests on experience. i) Justification/Confirmation trace to observation. ii) Meanings must translate into observational terms. distinction between theoretical and observational terms distinction between unobservable and observable entities Parsimony argument: 1) Evidence for T is evidence for T e (= empirical consequences of T) 2) No evidence justifies the part of T that goes beyond T e. b) Underdetermination argument. 1) Given evidence E, there are rival theories which entail E. 2) Any two of these, say T 1 and T 2, have the same justification (namely, E). 3) Hence, there is no reason to accept T 1 as true rather than T 2. (Again, what is confirmed is the common empirical part, T e.) c) Fallibilism/pessimistic induction. 1) Past theories have almost always been shown to be false. 2) Present/future theories are (inductively) likely to be false. 3) This skepticism is incompatible with accepting any theory as true. d) Quantum Mechanics Empirical consequences in excellent agreement with observation. Not clear what it would mean for the theory to be literally true. Solution: the theory is an instrument for prediction, not literally true. [And we should reason the same way for other theories.]

2 3. Some arguments for realism a) Inference to the best explanation/argument from success of science. 1. Present theories explain observed phenomena in a way that is objectively better than past rivals. 2. Hence, we are justified in taking them as more likely to be true or closer to the truth. Variant: If present theories were not approximately true, our technological success would be a miracle. b) Common cause argument. Common Cause Principle (CCP): When apparent coincidences occur that are too improbable to be attributed to chance, they can be explained by reference to a common causal antecedent. Example: food poisoning; barometer/storm; similar murders Application: Reality of molecules Perrin (1913): 13 independent methods for determining N (Avogadro s number). Agreement would be almost impossible if not for a common cause, the existence of molecules. Our wonder is aroused at the very remarkable agreement found between values derived from the consideration of such widely different phenomena. Seeing that not only is the same magnitude obtained by each method when the conditions under which it is applied are varied as much as possible, but that the numbers thus established also agree among themselves, without discrepancy, for all the methods employed, the real existence of the molecule is given a probability bordering on certainty. (Perrin, 1913) Atoms are no longer a useful fiction; things seem to us in favour of saying that we see them since we know how to count them The brilliant determinations of the number of atoms by M. Perrin have completed this triumph of atomism (Poincare, 1912) Hacking: How we see through a microscope visible grid, reduced to microscopic dimensions if shrunken grid is observable, so are microscopic objects Reasons for accepting reality of middle-sized objects become reasons to accept reality of microscopic objects

3 III. Maxwell: Ontological Status of Theoretical Entities I. Fictional scenario Some afflictions are transmitted by observable bugs (lice). Hypothesis: other infections spread by bugs ( crobes ) too small to be seen. Initial anti-realist responses: Instrumentalism. Crobes are devices for predictions. Operationalism. Statements about crobes are meaningful if translatable into sentences about what we d observe under operations. Problem: How maintain the distinction between observable and unobservable entities once microscopes are discovered and crobes are observed (and so seem on par with lice)? How maintain it in general, in response to the steady expansion of the observable? Anti-realist responses: i. Phenomenalism (primacy of sense-data). Both lice and crobes are unobservable. ii. Moderate anti-realism. Both lice and crobes are observable but some things (electrons? quarks?) are unobservable in principle. iii. Unaided observation. Lice are observable; crobes are not. We see only a shadow or image.

4 II. Attack on observational/theoretical distinction Main point: the distinction exists, but it is a contingent and evolving one that has no ontological significance. Note: Really, it s the observable/unobservable distinction that is Maxwell s target. Continuity argument Continuous series: windowpane : glasses : binoculars : : microscope. Continuous series: hydrogen : : huge (observable) polymers 1. There are observable objects about which we must be realists. 2. There are continuous series linking objects thought to be unobservable to observable objects. 3. We can t draw the line in a non-arbitrary way. Hence: we can t justify maintaining that there are unobservable objects about which we must be anti-realists. Objection: distinction is vague (cf. bald ), but not insignificant Response: it is insignificant because existence is not vague Question: The anti-realist isn t claiming that unobservable entities don t exist, just that we can t justify accepting their existence. Does this undercut Maxwell s argument?

5 Anti-realist responses 1. Refine the initial distinction (cf. moderate anti-realism). In principle observable vs. in principle unobservable In principle unobservable = unobservable according to theory. But if observable/unobservable distinction is theory-dependent, then there are no a priori criteria for separating observables from unobservables. Anything could become observable, even electrons (p. 1058). Question: Could we make the distinction relative to the final form of our scientific theories? 2. Actually observed vs. not actually observed Problem: items of a kind that has been observed should count as observable. Numerous technical difficulties. The view collapses to phenomenalism, the position that the only observables are sense data and things that can be constructed in terms of sense data. 3. Observable = sense data or construct (phenomenalism) Initial point: evidence statements used as basis for confirmation in science refer to physical objects, not sense data. [Sense data are actually theoretical entities: Sellars 1956] Significance: it s much harder to maintain a firm observable/unobservable distinction once we move beyond sense data, as the crobes story shows. Alternative: the confirmation basis should be characterized pragmatically in terms of quickly decidable sentences, and observational terms defined as those that occur in Q.D. sentences. Significance: we can train ourselves to observe entities that were once theoretical (e.g., sense data). Conclusion: We maintain a practical, evolving, contingent distinction between observational terms and theoretical terms. We can t divide observable entities from unobservable entities.