An Introduction to Critical Thinking and Creativity - always yours

84 VALID AND SOUND ARGUMENTS
9.4 SOUNDNESS
Given a valid argument, all we know is that if the premises are true, so is the conclusion.
But validity does not tell us whether the premises or the conclusion are
actually true. If an argument is valid, and all the premises are true, then it is called
a sound argument. Of course, it follows from such a definition that the conclusion
of a sound argument must be true. An argument that is not sound is unsound.
In a discussion, we should try out best to provide sound arguments to support
an opinion. The conclusion of the argument will be true, and anyone who disagree
would have to show that at least one premise is false, or the argument is invalid, or
both. This is not to say that we can define a good argument as a sound argument.
(We shall discuss this issue in chapter 12.)
EXERCISES
9.1 Is it possible to have valid arguments of the following types? If so can you
provide an example?
a) true premises, true conclusion
b) true premises, false conclusion
c) false premises, true conclusion
d) false premises, false conclusion
9.2 Are these statements true or false?
a) If the conclusion of this argument is true, then some or all the premises
are true.
b) If the premises of this argument are false, then the conclusion is also
false.
c) All sound arguments have true premises.
d) If an argument has a false conclusion, it cannot be sound.
e) If an argument is valid but unsound, its conclusion must be false.
f ) If all the premises and the conclusion of an argument are true, this still
does not imply that the argument is valid.
g) If the conclusion of a valid argument is true, the argument is sound.
h) If an argument is invalid, then whenever the premises are all false, the
conclusion must also be false.
i) If an argument is invalid, then it is possible for the conclusion to be false
when all the premises are true.