Download Report

Churchland vs. Van Fraassen
1
1. Background
1.1.
Churchland on Van Fraassen
Churchland: a theory’s overall or global success determines what we should accept at both the
theoretical and observational level.
Van Fraassen (according to Churchland): empirical success is “the only genuine measure of any theory’s
truth and that one’s acceptance of a theory should create no ontological commitments whatever
beyond the observational level.” (35)
Van Fraassen (in his own words): “Science aims to give us theories which are empirically adequate; and
acceptance of a theory involves as belief only that it is empirically adequate.”
1.2.
Churchland’s Objectives
To argue that “ontological commitments of any theory are wholly blind to the idiosyncratic
distinction between what is and what is not humanly possible.”
To argue that “empirical adequacy is only one epistemic virtue among others of equal or comparable
importance.” The other virtues include simplicity, coherence, and explanatory power.
2. Observation and Ontology
2.1.
Churchland’s Argument: Big Picture
C1. If constructive empiricism is true, then agnosticism about unobservables is more reasonable than
agnosticism about observables.
C2. Agnosticism about unobservables is just as reasonable as agnosticism about observables.
C3. ∴ Constructive empiricism is not true.
2.2.
Van Fraassen’s Argument for C1
1. If constructive empiricism is true, then theoretical (superempirical) virtues such as simplicity,
coherence, and explanatory power are pragmatic, but are not epistemic. (Note that this figures in
§3)
2. If theoretical virtues are not epistemic, then the only measure of any theory’s truth is empirical
adequacy.
3. If the only measure of any theory’s truth is empirical adequacy, then agnosticism about
observables is unreasonable.
4. ∴ If constructive empiricism is true, then agnosticism about observables is unreasonable. (From
1-3)
5. If the only measure of any theory’s truth is empirical adequacy, and T is empirically adequate
with respect to some empirical domain D, then there will always be other acceptable theories T*
that are also empirically adequate with respect to D, but which have radically different nonobservational ontologies. (Non-observational ontology is “underdetermined” with respect to the
phenomena in D.)
6. If, for all domains D, there will always be other acceptable theories T* that are also empirically
adequate with respect to D, but which have radically different non-observational ontologies, then
agnosticism about any particular unobservables is reasonable.
7. ∴ If constructive empiricism is true, then agnosticism about any particular unobservables is
reasonable. (From 1,2,5,6)
C1. ∴ If constructive empiricism is true, then agnosticism about unobservables is more reasonable
than agnosticism about observables. (From 4,7)
2.3.
Churchland’s ‘Theory-Ladenness’ Argument for C2
1. The meaning of observational terms is partially determined by theoretical presuppositions.
(Observation is “theory-laden.”)
2. If the meaning of observational terms is partially determined by theoretical presuppositions, then
observational ontology and non-observational (theoretical) ontology are mutually dependent.
3. If observational ontology and non-observational ontology are mutually dependent, then
agnosticism about unobservables is just as reasonable as agnosticism about observables.
C2. ∴ Agnosticism about unobservables is just as reasonable as agnosticism about observables.
(From 1-3)
Churchland vs. Van Fraassen
2
2.4.
Churchland’s ‘Control’ Argument for C2
1. If it is contingently true that, for many x, humans have more control over their spatiotemporal
proximity to x than over the size1 of x, then there is only a practical point in calling
spatiotemporally distant but otherwise perceptible entities “observable;” and calling
imperceptibly small (or large) entities “unobservable.”
2. It is contingently true that, for many x, humans have more control over their spatiotemporal
proximity to x than over the size of x.
3. If there is only a practical point in calling some things “observable” and other things
“unobservable”, then agnosticism about unobservables is just as reasonable as agnosticism about
observables.
C2. ∴ Agnosticism about unobservables is just as reasonable as agnosticism about observables.
(From 1-3)
3. The Theoretical (‘Superempirical’) Virtues
3.1.
Theory-Ladenness Argument for the Virtues
1. There are times when two theories are so different that they lack a common empirical vocabulary
(i.e. are incommensurable.)
2. If two theories lack a common empirical vocabulary, then there is no empirical evidence that
could adjudicate between them.
3. If no empirical evidence can adjudicate between two theories, then the theoretical virtues must
adjudicate between them.
4. ∴ There are times that the theoretical virtues adjudicate between two theories that lack a
common empirical vocabulary. (From 1-3)
5. If the theoretical virtues adjudicate between two theories that lack a common empirical
vocabulary, then the theoretical virtues determine the appropriate empirical vocabulary.
6. If theoretical virtues determine the appropriate vocabulary, then the theoretical virtues are at
least as epistemic as empirical adequacy.
7. ∴ There are times when the theoretical virtues are at least as epistemic as the theoretical virtues.
3.2.
‘Weak Cyborg’ Argument
1. Suppose that there is a community of cyborgs whose sensory organs have all been replaced by
detectors that feed beliefs direct to their brains. Additionally, these beliefs are exactly the same
beliefs that a human with normal sensory organs would form under the same circumstances.
2. If van Fraassen’s account of observability is correct, then the cyborg community observes
nothing.
3. If a community observes nothing, then their theories cannot be empirically adequate.
4. ∴ If van Fraassen’s account of observability is correct, the cyborg community cannot have
empirically adequate theories. (From 1-3)
5. It is possible that the cyborg community has theories that successfully explain and predict the
spontaneous beliefs delivered by their detectors.
6. Either empirical adequacy or the theoretical virtues make explanations and predictions
successful.
7. ∴ If van Fraassen’s account of observability is correct, then theoretical virtues make the cyborg
community’s explanations and predictions successful. (From 4-6)
8. If theoretical virtues make the cyborg community’s explanations and predictions successful, then
theoretical virtues are epistemic.
C5. ∴ If van Fraassen’s account of observability is correct, then theoretical virtues are epistemic.
(From 7,8)
Discussion: Clearly, van Fraassen should accept this argument unless he can find fault with its basic
premises (1-3,5,6,8—can you see anything wrong with these assumptions?) Additionally, however,
Churchland lists energy, length, and mass as other aspects of an entity over which we have relatively
little control. The argument works for them, too.
1
Churchland vs. Van Fraassen
3
Churchland suggests that if one rejects Premise 2, and claims that the cyborgs’ spontaneous beliefs
count as observations, then Churchland does “not see how we can justify van Fraassen’s selective
skepticism with respect to the wealth of ‘unobservable’ entities and properties reliably monitored by
our transducing instruments (electron microscopes, cloud chambers, chromatographs, etc.)” Agree or
disagree?
4. ‘Humanoid’ Argument against van Fraassen’s Observable-Unobservable Distinction
1. Suppose that humanoids are born with the biological equivalent of an electron microscope in
place of their left eyes.
2. Then the humanoids can observe viruses, DNA, etc.
3. If constructive empiricism is true, then agnosticism about observables is unreasonable (see §2.2.)
4. ∴ If constructive empiricism is true, then the humanoids are unreasonable if they are agnostic
about the existence of viruses, DNA, etc. (From 1-3)
5. If the causal connections and experiences of two perceptual processes P1 and P2 are identical,
then it is just as reasonable to believe the outputs of P1 as it is to believe the outputs of P2.
6. The causal connections and experiences of the humanoids’ and our detection of viruses, DNA,
etc. are identical.
7. ∴ If constructive empiricism is true, then we are unreasonable if we are agnostic about the
existence of viruses, DNA, etc. (From 4-6)
8. If constructive empiricism is true, then we are reasonable if we are agnostic about the existence of
viruses, DNA, etc.
9. ∴ Constructive empiricism is not true (From 7, 8)
5. Churchland’s Pragmatic Realism
Churchland agrees with van Fraassen that: (4.1) science is a matter of construction rather than
discovery, and (4.2.) truth is not the science’s aim.
5.1.
Constructive realism
For Churchland, mental activity is best regarded as brain activity (see his essay on Eliminative
Materialism). Brain activity is constructive, e.g. synapses are formed.
5.2.
Realism without the aim of truth
Van Fraassen has a more modest scientific aim than truth—empirical adequacy.
By contrast, Churchland opts for “pragmatism,” in which scientific success is to be measured by
“reproductively advantageous behavior”. Thus, he thinks that science’s success is ultimately to be
measured in evolutionary terms.
1. If truth is the aim of science, then beliefs and propositions should be part of our scientific
ontology.
2. Beliefs and propositions should not be part of our scientific ontology. (See “Eliminative
Materialism”)
3. ∴ Truth is not the aim of science.
5.3.
Is this still realism?
1. If Churchland’s pragmatism is true, then scientific success consists is measured by reproductively
successful behavior.
2. There is “some connection between the faithfulness of the brain’s ‘world-model’” and
reproductively successful behavior.
3. If Churchland’s pragmatism is true, then scientific success requires a faithful model of the world.
4. If scientific success requires a faithful model of the world, then realism is true.
5. ∴Churchland’s pragmatism is a kind of realism.
6. Van Fraassen’s Replies to Churchland
Observability = whatever members of our epistemic community can detect with their senses without
technological aids.
6.1.
Cyborgs
The cyborgs can detect less with their senses without technological aids than members of our
epistemic community. So anything that is observable to them is observable to us.
Churchland vs. Van Fraassen
4
6.2.
Superhumans
1. If the humanoids are part of our epistemic community, then our notion of observability will
change accordingly: viruses, DNA, etc. will become observable. (see van Fraassen’s discussion of
the statement “If the epistemic community changes in fashion Y, then my beliefs about the
world will change in manner Z.”)
2. If DNA, etc. are observable, then Premise 8 of Churchland’s Humanoid Argument is false:
constructive empiricism can be true even if we are unreasonable if we’re agnostic about DNA,
etc. (because ‘we’ now includes both humans and humanoids.)
3. ∴ If the humanoids are part of our epistemic community, then Churchland’s Humanoid
Argument is unsound. (From 1,2)
4. If the humanoids are not part of our epistemic community, then we will have to form a theory
about how their left eye works, and that theory simply has to be empirically adequate.
5. If we only need an empirically adequate theory of how their left eyes work, then Premise 7 of
Churchland’s Humanoid Argument is false: constructive empiricism can be true even if we’re
reasonable in being agnostic about DNA, etc.
6. ∴ If the humanoids are not part of our epistemic community, then Churchland’s Humanoid
Argument is unsound. (From 4,5)
7. Either the humanoids are part of our epistemic community or they are not.
8. ∴ Churchland’s Humanoid Argument is unsound (from 3,6,7)
6.3.
Virtues
1. If simplicity2 is a property of a theory, then it has no connection to the world.
2. If simplicity has no connection to the world, then it is not epistemic.
3. ∴ If simplicity is a property of a theory, then it is not epistemic.
4. If simplicity is a property of the world, then there are still many simple false theories.
5. If there are many simple false theories, simplicity is not epistemic.
6. ∴ If simplicity is a property of the world, then it is not epistemic.
7. Either simplicity is a property of a theory or it is a property of the world
8. ∴ Simplicity is not epistemic.
2
Van Fraassen suggests that this objection would apply to all other theoretical virtues too.