Intro to Logic - Question
"D. Which of the following is possible? If it is possible, give an example. If it is not possible, explain why.
4. An invalid argument, the conclusion of which is a tautology."
Rocks are dense.
Rocks are heavy.
Therefore, rocks are either rough, or they're not.
Correct answer: Not possible.
Where did I go wrong?
There was another question I wasn't too sure of, however the textbook didn't give an answer for this one. The question is:
"B. For each of the following: Is it a tautology, a contradiction, or a contingent sentence?
6. If anyone has ever crossed the Rubicon, it was Caesar."
My answer: Contradiction.
Is this correct?