Argument Valid? Type of Argument EXAMPLE: (1) If Joe can be president, he is 35 or older. (2) Joe is 35 or older. (3) Therefore, Joe can be president. Invalid This is an example of affirming the consequent. Being 35 or older is a necessary, but not sufficient condition for being president. He or she must also be a natural born U.S. citizen and not a felon. (1) If Sally is farsighted, then she needs glasses. (2) Sally does not need glasses. (3) Therefore, Sally is not farsighted. Invalid This is an example of inductive argument. The conclusion (the second and the third alternatives) do not support the premise. Being farsighted is not the only reason why an individual may or may not need glasses. Sally may need glasses, but she may not be farsighted. Probably, she might have other sight problems. Alternatively, Sally may not need glasses, but this does not mean that she does not have sight problems. She might have other sight problems, whose remedies are not necessarily glasses. (1) If Joe plays football in the NFL, then he’s a professional athlete. (2) Joe does not play football in the NFL. (3) Therefore, Joe is not a professional athlete. Invalid This is also an example if inductive argument whereby, what the premise provides or appears to provide is not supported by the conclusion. An individual does not have to play football in NFL to be a professional athlete. There are other football clubs where professional athletes play. Joe can be playing football in other football clubs apart from NFL, which recruit professional athletes. (1) If Sally is in Tokyo, then she’s in Japan. (2) Sally is in Tokyo. (3) Therefore, Sally is in Japan. Valid This is an example of deductive argument. What the premise provides or appears to provide, is supported by the conclusion. Tokyo is the capital city of Japan. Therefore, if an individual is in Tokyo, then that person is inside Japan.

 Type Your Argument Hypothetical Syllogism If it rains, we will not go camping. If we do not go camping, then we do not need a tent. If it rains, we do not need a tent. If my sister passes her interview, I will owe her a present. If I owe her a present, I will need to go shopping. If my sister passes her interview, I will go shopping. Disjunctive Syllogism The chef used either salt or lemon to season the food. The chef did not use salt to season the food. Therefore, the food has been seasoned with lemon. Either the sun goes round the moon, or the moon goes round the sun. The moon does not go round the sun. Therefore, the sun goes round the moon. Constructive Dilemma I must either run or walk through the fire. If I walk, I shall catch fire immediately. Nevertheless, if I run, I shall be catch fire immediately. Therefore, I shall catch fire. We must either swim or use a boat to get to other side of the river. If we swim, we shall get to the other side. If we use a boat, we shall also get to the other side of the river. Therefore, we shall get to the other side of the river.

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