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| − | A '''valid argument''', in [[formal logic]], one in which the conclusion is correctly derived from the premises. | + | A '''valid argument''', in [[formal logic]], one in which the conclusion is correctly derived from the premises. That is, a valid argument is one in which, if the premises are true, the conclusion must also be true. A valid argument whose premises are true is called a '''sound argument''', and its conclusion must be true. |
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| + | A valid argument whose premises are not all true is called a '''valid but unsound argument''', and its conclusion is not necessarily true. The following is an example of a valid but unsound argument, in which one of the premises is untrue, so that the conclusion cannot be relied upon (and is wrong): | ||
| + | *Grass is green. | ||
| + | *All green things taste like limes. (untrue premise) | ||
| + | *Therefore, grass tastes like limes. | ||
{{quotebox|A deductive argument is said to be valid when the inference from premises to conclusion is perfect. [http://www.philosophypages.com/lg/e01.htm Arguments and Inference: truth and validity] }} | {{quotebox|A deductive argument is said to be valid when the inference from premises to conclusion is perfect. [http://www.philosophypages.com/lg/e01.htm Arguments and Inference: truth and validity] }} | ||
[[Category:Logic]] | [[Category:Logic]] | ||
Latest revision as of 20:57, September 12, 2019
A valid argument, in formal logic, one in which the conclusion is correctly derived from the premises. That is, a valid argument is one in which, if the premises are true, the conclusion must also be true. A valid argument whose premises are true is called a sound argument, and its conclusion must be true.
A valid argument whose premises are not all true is called a valid but unsound argument, and its conclusion is not necessarily true. The following is an example of a valid but unsound argument, in which one of the premises is untrue, so that the conclusion cannot be relied upon (and is wrong):
- Grass is green.
- All green things taste like limes. (untrue premise)
- Therefore, grass tastes like limes.
A deductive argument is said to be valid when the inference from premises to conclusion is perfect. Arguments and Inference: truth and validity