1. TRUTH TABLE TO DETERMINE
THE VALIDITY OF AN ARGUMENT

2. The maid has been arrested. She is accused of murdering
Uncle Alfred. Her trial is about to begin.

3. The prosecutor presents his argument:
If there are fingerprints on the gun then the butler is the murderer.
There are NO fingerprints on the gun.
Either the butler is the murderer or the maid did it.
Therefore, the maid did it!

4. Fortunately, the maid’s lawyer took this course - and with the
following truth table, she proves that the prosecutor’s argument
is INVALID!

5. THE PROSECUTOR’S
ARGUMENT:
If there are fingerprints on the gun then the butler is the murderer.
There are NO fingerprints on the gun.
Either the butler is the murderer or the maid did it.
Therefore the maid did it.

11. The premises might all be true
and you would not have to believe the conclusion

12. The argument is INVALID
The premises might all be true
and you would not have to believe the conclusion