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14. Science / C. Induction / 5. Paradoxes of Induction / b. Raven paradox

[problem irrelevant evidence for a general law]

16 ideas
Read 'all ravens are black' as about ravens, not as about an implication [Belnap]
     Full Idea: 'All ravens are black' might profitably be read as saying not that being a raven 'implies' being black, but rather something more like 'Consider the ravens: each one is black'.
     From: Nuel D. Belnap (Conditional Assertion and Restricted Quantification [1970], p.7), quoted by Stephen Yablo - Aboutness 04.5
     A reaction: Belnap is more interested in the logic than in the paradox of confirmation, since he evidently thinks that universal generalisations should not be read as implications. I like Belnap's suggestion.
The raven paradox has three disjuncts, confirmed by confirming any one of them [Armstrong]
     Full Idea: We could rewrite the generalisation as For all x, ((x is a raven and x is black) v (x is not a raven and x is black) v (x is not a raven and x is not black)). Instances of any one of the three disjuncts will do as confirmation.
     From: David M. Armstrong (What is a Law of Nature? [1983], 04.3)
     A reaction: A nice clarification.
It is because ravens are birds that their species and their colour might be connected [Harré]
     Full Idea: It is because ravens are birds that it makes sense to contemplate the possibility of a lawful relation between their species and their colour.
     From: Rom Harré (Laws of Nature [1993], 5)
     A reaction: Compare the 'laws' concerning leaf colour in autumn, and the 'laws' concerning packaging colour in supermarkets. Harré's underlying point is that raven colour concerns mechanism.
Non-black non-ravens just aren't part of the presuppositions of 'all ravens are black' [Harré]
     Full Idea: Non-black non-ravens have no role to play in assessing the plausibility of 'All ravens are black' because their existence is not among the existential presuppositions of that statement.
     From: Rom Harré (Laws of Nature [1993], 5)
     A reaction: [He cites Strawson for the 'presupposition' approach]
Contraposition may be equivalent in truth, but not true in nature, because of irrelevant predicates [Harré/Madden]
     Full Idea: The question about Hempel's Paradox is whether contraposition is not only equivalent in truth, but equivalent tout court. It forcibly inserts new predicates into a context of properties known to be connected by nature.
     From: Harré,R./Madden,E.H. (Causal Powers [1975], 7.I)
     A reaction: [compressed] This seems to capture quite nicely the intuition most people have (which makes it a 'paradox') that the equivalent predicate is irrelevant to the immediate enquiry. The paradox is good because it forces the present explanation.
The items put forward by the contraposition belong within different natural clusters [Harré/Madden]
     Full Idea: If empirical predicates are linked in clusters, contraposition of (black, raven) would carry one via such pairs as (shoe, white) into a different empirical cluster, or no cluster at all.
     From: Harré,R./Madden,E.H. (Causal Powers [1975], 7.I)
     A reaction: This is, of course, addressed to Hempel's Raven Paradox. Those paradoxes now strike me as relics of a time when Humean empiricism and logic were thought to be the best approaches to scientific theory. Harré and Madden pioneered a better view.
The possibility that all ravens are black is a law depends on a mechanism producing the blackness [Harré/Madden]
     Full Idea: The generating mechanism that produces black raven-like beings is assumed in the according of potential law status to the statement that all ravens are black.
     From: Harré,R./Madden,E.H. (Causal Powers [1975], 7.III)
     A reaction: This is a very nice succinct statement of what I take to be the scientific essentialist view of induction. It isn't about building up Humean habits of regularity, but of gradually inferring explanatory mechanisms, which might even give necessities.
If something in ravens makes them black, it may be essential (definitive of ravens) [Lipton]
     Full Idea: We are considering that there is something in ravens, a gene perhaps, that makes them black, and this cause is part of the essence of ravens. Birds lacking this cause could not interbreed with ravens.
     From: Peter Lipton (Inference to the Best Explanation (2nd) [2004], 05 'Unsuitable')
     A reaction: At last, the essentialist approach to induction! Of course, it is tricky to decide a priori whether there could be albino ravens. It only takes one white (interbreeding) raven to ruin a nice essentialist story. Individuals matter.
My shoes are not white because they lack some black essence of ravens [Lipton]
     Full Idea: The reason my shoe is white is not that it lacks some feature essential to ravens that makes them black.
     From: Peter Lipton (Inference to the Best Explanation (2nd) [2004], 06 'The Method')
     A reaction: Good, but not totally true. If my shoes were made to grow from genes, and then had some raven spliced into them, we might manage it. That is an explanation, but a long way from the best one. Enquiry is explanations, not deductions.
A theory may explain the blackness of a raven, but say nothing about the whiteness of shoes [Lipton]
     Full Idea: Explanatory considerations help with the raven paradox since, while the raven hypothesis may provide an explanation for the blackness of a particular raven, neither the original hypothesis nor its contrastive explanation explain why the shoe is white.
     From: Peter Lipton (Inference to the Best Explanation (2nd) [2004], 06 'Unsuitable')
     A reaction: For me, the examination of ravens is a search for the essence of ravenhood, which is why non-ravens don't help. Of course, if you eliminate all culprits except one, you have your culprit, but will your evidence stand up in court?
We can't turn non-black non-ravens into ravens, to test the theory [Lipton]
     Full Idea: We cannot transform a non-black non-raven into a raven to see whether we get a simultaneous transformation from non-black to black, in the way we can transform a flame without sodium into a flame with sodium.
     From: Peter Lipton (Inference to the Best Explanation (2nd) [2004], 06 'Unsuitable')
     A reaction: A white shoe would be an example of a non-black non-raven. People mesmerised by the raven paradox are too concerned with investigation being a 'logical' process. Lipton makes a nice point. We need to know the nature of ravens.
To pick a suitable contrast to ravens, we need a hypothesis about their genes [Lipton]
     Full Idea: Without something like a hypothesis about the genes of ravens, we simply do not know what would count as a relevantly similar bird for comparison.
     From: Peter Lipton (Inference to the Best Explanation (2nd) [2004], 06 'Unsuitable')
     A reaction: Lipton is endorsing the view that explanation should be 'contrastive', as well as aiming to discover the inner nature of ravens. He makes a good case for the contrastive approach.
If sentences point to different evidence, they must have different subject-matter [Yablo]
     Full Idea: 'All crows are black' cannot say quite the same as 'All non-black things are non-crows', for the two are confirmed by different evidence. Subject matter looks to be the distinguishing feature. One is about crows, the other not.
     From: Stephen Yablo (Aboutness [2014], Intro)
     A reaction: You might reply that they are confirmed by the same evidence (but only in its unobtainable totality). The point, I think, is that the sentences invite you to start your search in different places.
Most people say nonblack nonravens do confirm 'all ravens are black', but only a tiny bit [Yablo]
     Full Idea: The standard response to the raven paradox is to say that a nonblack nonraven does confirm that all ravens are black. But it confirms it just the teeniest little bit - not as much as a black raven does.
     From: Stephen Yablo (Aboutness [2014], 06.5)
     A reaction: It depends on the proportion between the relevant items. How do you confirm 'all the large animals in this zoo are mammals'? Check for size every animal which is obviously not a mammal?
'All x are y' is equivalent to 'all non-y are non-x', so observing paper is white confirms 'ravens are black' [Mautner, by PG]
     Full Idea: If observing a white sheet of paper confirms that 'all non-black things are non-ravens', and that is logically equivalent to 'all ravens are black' (which it is), then the latter proposition is confirmed by irrelevant observations.
     From: report of Thomas Mautner (Penguin Dictionary of Philosophy [1996], p.105) by PG - Db (ideas)
     A reaction: This seems to me more significant than the 'grue' paradox. If some observations can be totally irrelevant (except to God?), then some observations are much more relevant than others, so relevance is a crucial aspect of induction.
Observing irrelevant items supports both 'all x are y' and 'all x are non-y', revealing its absurdity [Schofield,J]
     Full Idea: Although Hempel's raven paradox produces an absurdity of irrelevant observations, we can ignore it because (unlike good observations) observing a white handbag supports the contradictions of 'ravens are black' and 'ravens are non-black'.
     From: Jonathan Schofield (talk [2005]), quoted by PG - Db (ideas)
     A reaction: The idea of 'eliminating it from our enquiries' cannot be totally irrational (e.g. in detective work), but it is only seriously sensible in a restricted domain (such as a country house)