What is the Paradox of the Ravens and why is it important?
Science is a complicated yet extravagant division in the development of knowledge. Philosophers have tried to explain the complex scientific methods used to demonstrate the importance of how a scientific method requires immunity to criticism. A philosopher, who indeed, did question a method in order to gain a complete understanding, was Carl Gustav Hempel. Hempel challenged the theory of induction in which he recognized a problem with the definition and application of inductive logic. Inductive logic seemed to defy the apparent ability of knowledge without assumptions or the use of reasoning. This was the preliminary aspect of what we now call the Raven paradox. The Raven Paradox is the most common title used in preference to ‘Hempel’s Paradox’ or the ‘Paradox of confirmation’. Hempel’s Raven Paradox was initially established to question the methods of induction. Through a carefully selected scientific procedure, Hempel aimed to highlight the concepts of how inductive reasoning was a source of violation towards intuition and common sense. Firstly, what is induction? Induction is a form of reasoning in which a problem is analysed by developing facts and instances that result in a conclusion, which does not necessarily have to be true. The principle of induction allows for great generalizations that are easily supported and confirmed by evidence. Hempel approached his questioning with a hypothetical statement, ‘All ravens are black’. This hypothesis has a logically equivalent hypothesis, “All non-black objects are non-raven”. Since these two hypotheses have logical equivalence, they should easily be confirmed by the same instances, or evidence. (Hempel 1945) Hempel applied Nicod’s criterion to his example that resolves as the Raven Paradox. The criterion produced by Jean Nicod was to describe how one statement can confirm another. ‘All A are B’ can be confirmed by objects that are both A and B. The hypothesis will be rejected by objects that are A but not B. Objects that are not A are irrelevant. Hempel came up with the ‘equivalence condition’ in which he noted that if a certain set of instances could confirm or disconfirm a hypothesis, it should also be able to act as an instance towards the logically equivalent hypothesis. The example “All ravens are black” (A) demonstrates that the evidence used to prove this hypothesis would equally satisfy the logically equivalent hypothesis, “All non-black objects are non-ravens” (B) and vice versa. (A) can easily be confirmed by instances in which black ravens have been observed and as it is direct, it acts as strong evidence. The paradox is highlighted here, where Hempel notes that when both (A) and (B) are logically equivalent, by the Law of Contrapositives, they should be equally confirmed by instances that support one statement, even if it seems illogical (Dunbar, 1995). This means, that just as a black raven supports (A), observation of a yellow lemon will serve as evidence to (A) as a yellow lemon is both a non-black object and a non-raven, it supports (B). Since (B) is logically equivalent to A, the observation of a yellow lemon would ideally serve as evidence to the hypothesis, “All ravens are black”. ‘All Fs are G’ would be supported by the observation of an F that is also G. But if this is generally true, then the discovery of a non-black non-raven (E.g., a white shoe) confirms that all non-black things are non-ravens; and thereby confirms the logically equivalent hypothesis. “all ravens are black’- a seemingly bizarre conclusion. This is ‘the paradox of confirmation’. (Curd & Cover, 1998, p.608) But, why should observation of a non-black, non-raven such as a yellow lemon serve as evidence to the statement that all ravens are black? This perception seems irrelevant, illogical and counter-intuitive to the initial hypothesis. This may seem illogical but there is no procedure that proves the method incorrect....
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Godfrey-Smith, P 2003, An introduction to the philosophy of science; Theory and reality, The University of Chicago Press, USA.
Hempel, CG 1945, Studies in the Logic of Confirmation I. Mind Vol 54
Howson, C & Urbach, P 1989, Scientific reasoning: The Bayesian approach, Open Court Publishing Company, USA.
Philosophy dictionary, 2005, Oxford University Press, England.
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