PHIL 102 Lecture Notes - Lecture 2: Modus Ponens, Modus Tollens, Logical Form
28 Sep 2016
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If sara is a western student ,then sara is smart. The second line is the same as the if clause of line 1. The third line is the same as the then clause of line 1. A and b are variables and can be replaced with any statement. 1. if dennis is a human (a), then dennis is an animal(b) Substitution instance - an argument form that is caused by uniformly replacing letters in that argument form with statements. Formally valid - an argument that is valid in virtue of its form. Valid argument form- an argument where every substitution instance is a valid argument. Some arguments can be valid in virtue of form but not all are. This argument is valid but only because the conclusion is a necessary truth. The validity has noting to do with its form. The form of this argument is: a, so b. This form is wrong is does not always produce valid arguments.
