A is a sound argument.
by the definition of sound, A is both (1) valid and (2) has only true premises.
because A has only true premises, A has no false premises.
an argument A has false premises.
by the definition of "valid", A cannot have true premises and a false conclusion.
Suppose       __________
Then,      __________
So, finally,      __________
Q.E.D.

1.3ex III
Informal Proofs

Matching. Drag sentences from the right to the correct location in the proof box. Don't print until you've come to the final page of this exercise.

First show that...

1. A sound argument has no false premises.