The Deductive-Nomological Model: a Critcism

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The most recent discussions in the field of philosophy of science on scientific explanation began in the 1940s with Hempel’s deductive-nomological model (D-N model). According to Hempel the following four adequacy conditions must met in order to qualify as a D-N explanation: 1. The explanation must be a valid deductive argument, with the thing to be explained as its conclusion. 2. The explanans must contain at least one general law that is required for the conclusion. 3. The explanans must have empirical content that is testable. 4. The statements of the explanans must be true. All four conditions when met are individually necessary and justifiably sufficient to be considered scientific explanations so D-N explanations are scientific explanations. All D-N explanations are arguments that demonstrate that if the explanans are available prior to the conclusion it is possible to predict the conclusion. So it can be said that every D-N explanation can potentially predict an event. Immediately, based in this information the D-N model suffers from a problem because condition number 2 states D-N explanations require adherence to a general law but predictions can also be made based on correlations. This issue is a minor matter that does not negate the D-N model on its own; however, the problems for the D-N model do not stop there. Nowhere in the model does cause factor into an explanation. Consider this counterexample: 1. People with Down syndrome have Trisomy 21. 2. Josh has Down syndrome. Josh has Trisomy 21. While this counterexample satisfies the conditions of the D-N model it explains a cause using the effect rather than explaining the effect by means of the cause. This lack of account for causal influences makes this D-N argument stray into the realm of inaccuracy. Another problem that arises with the D-N model is when all four adequacy conditions
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