Premise 1
Premise 2
Premise 3
…
-----------------
Conclusion
An argument is valid if and only if it is impossible for the premises to be true and the conclusion false."Sound" Arguments:
An argument is sound if and only if it is valid and the premises are true.So, there are two ways for an argument to be bad:
(i) One (or more) of the premises could be false
(ii) The premises could fail to support the conclusion. (There could be some gap in the reasoning).
Example 1:This is a good argument. It is valid and since the premises are true, it is also sound.
Premise 1 St. Paul is a city in Minnesota.
Premise 2 Last week I was in St. Paul.
------------
Conclusion Therefore, last week I was in Minnesota.
Example 2:This is a valid argument, but since the premises are false, it is not sound.
Premise 1 I am the star player on Carolina's basketball team
Premise 2 Everyone on Carolina's basketball team is over 7 feet tall.
------------
Conclusion Therefore, I am over 7 feet tall
Example 3:This argument is not valid (and so, even if the premises are true, it is also not sound). It's possible that both of the premises are true, but the conclusion is false. (For example, if there's a problem with the starter the car could fail to start even though the battery is not dead.)
Premise 1 If my car's battery is dead, then my car won't start.
Premise 2 My car won't start.
------------
Conclusion Therefore, my battery is dead.