Exercises

I. Directions:. Determine whether each of the following arguments is valid. If an argument is invalid, explain why.

1. All mammals have fur.
    Lassie is a mammal.
    Therefore, Lassie has fur.

2. Either Sam buys Marissa a ring or Vanessa buys Sam a ring.
    Sam does not buy Marissa a ring.
    Therefore, Vanessa buys Sam a ring.

3. If Jason gives Eric $5, then Eric gives Carrie $2.
    If Eric gives Carrie $2, then Carrie gives Ellen $1.
    Therefore, if Carrie gives Ellen $1, then Jason gives Eric $5.

4. Molly is a cow.
    Molly has horns and wears a cowbell.
    Cowbells are used to keep track of cows.
    Molly’s cowbell is loud.
    Therefore, Molly wears a cowbell.

5. If Mr. Potatohead comes to life, then he will frighten children.
    Mr. Potatohead will not frighten children.
    Therefore, Mr. Potatohead does not come to life.

6. Jacob has a lion tattoo.
    Max has a pottery wheel.
    Therefore, Jacob has a lion tattoo and Max has a clay pot.

7. The Stanford Bulletin can be used to prop up rickety furniture.
    Therefore, the Stanford Bulletin can be used to prop up rickety furniture or to decide which classes     you should be taking.

II. Directions: Determine whether each of the following arguments is sound.  If an argument is unsound, explain why.

1. All fish can swim and have gills.
    A salmon is a fish.
    Salmon can swim and have gills.

2. If Martha Stewart is the President of the United States, then the country is doomed.
    Martha Stewart is the President of the United States.
    Therefore, the country is doomed.

3. Elisa dyes her hair blond or Jessica dyes her hair green.
    Elisa dyes her hair blond.
    Therefore, Jessica does not dye her hair green.

VIII. Solutions to Practice Exercises