Introductory Logic
Quiz #1
February 17, 2006
 
Name: ________________________
R. Hammack
Score: _________

1. Three arguments are given. For each one, underline the conclusion. Then say if the argument is deductive, inductive, valid, invalid, weak, strong, and (if possible) sound, unsound, cogent, or uncogent.

(a)
 Traffic is usually congested in Northern Virginia, so I will be delayed when I drive through Washington D.C. during rush hour this evening.

INDUCTIVE, STRONG, COGENT


(b)
 Since Shakespeare wrote many plays, it follows that he was literate, for anyone who can write a play is literate.

DEDUCTIVE, VALID, SOUND


(c)
 Twenty percent of Americans are senior citizens. Therefore about twenty percent of college students are senior citizens.

INDUCTIVE, WEAK, UNCOGENT



2. Use the counterexample method to show that the following argument is invalid.

  Some existentialist poets are geniuses, for some madmen are existentialist poets, and all geniuses are madmen.


Argument:

P: Some madmen are existentialist poets.
P: All geniuses are madmen.
C: Some existentialist poets are geniuses.		 Substitution Instance:

M = "Animals"
E = "Cats"
G = "Dogs"

Argument Form:

Some M are E.
All G are M.
Thus some E are G.

 Some animals are cats.
All dogs are animals.
Thus some cats are dogs.

The argument now has true premises
and false conclusion. It's INVALID.