PHIL 430 Lecture Notes - Lecture 4: Modus Tollens, Fetus, Modus Ponens
Document Summary
A valid argument is one where the conclusion must be true if its premises were all true. A sound argument is a valid argument with all actually true premises. Some common valid argument forms: all a"s are b"s, all b"s are c"s, so, all a"s are c"s. A venn diagram illustrates this: all a"s are b"s, x is a, so, x is b. Any argument in this form is valid. (this argument form is very common: it"s known as modus ponens) It"s a little trickier to see why this is a valid argument form, but it is: any argument in this form is valid. (this argument form is also very common: it"s known as modus tollens) Practice: shaq is 7 feet 1 inches tall. 2: so, shaq is less than 8 feet tall. If shaq is 7 feet 1 inches tall, then shaq is less than 8 feet tall. If chuck norris is in boston, then he"s in mass.
