Unformatted text preview: Validity, soundness, strength, cogency Deductive arguments Factual claim Inferential claim Soundness Validity Validity Addresses whether the premises provide support for the conclusion. In a valid argument if the premises are true the conclusion has to be true. Validity is not connected with truth. How to test for validity Assume the premises are true. Based on that assumption ask: Does the conclusion have to be true? If the answer is yes the argument is valid. If the answer is no the argument is invalid. An argument with actually true premises and a false conclusion is always invalid. Soundness Addresses the truth of the premises. To determine soundness simply ask: Are the premises REALLY true? Do not assume the premise are true this only applies to validity. Invalid arguments are ALWAYS unsound. Inductive arguments Factual claim Inferential claim Cogency Strength Strength Unlike validity strength is a term of degree. An argument is strong if the premises provide probable support for the conclusion. In general if the probability for the conclusion to follow from the premises is greater than 50% the argument is strong. How to test for strength Assume the premises are true. Based on this assumption ask: Is the conclusion probably true? If the answer is yes the argument is strong. If the answer is no the argument is weak. Cogency Addresses the actual truth of the premises. To determine cogency ask: Are the premises REALLY true? If the answer is yes the argument is cogent. If the answer is no the argument is uncogent. Weak arguments are ALWAYS uncogent. Total evidence requirement In cogent inductive arguments the premises must not only be true but also not ignore any important evidence that would entail a different conclusion. Do not confuse the terms! Deductive Valid/Invalid Sound/Unsound Inductive Strong/Weak Cogent/Uncogent ...
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 Spring '07
 D.C.
 Logic, premises

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