The logic challenge
If you’re still having your doubts about logic, then I have a couple of challenges for you. The first challenge is this: Take a piece of paper and draw a four-sided triangle. The second challenge is this: Take a piece of paper and draw three straight lines, labeled A, B, and C, such that A is longer than B, B is longer than C, and C is longer than A. When you fail, ask yourself why. (Hint: Both challenges entail logical contradictions.) You will notice that logic is not a mere matter of language. It actually applies to the external world. You need not search the universe to see if there are any four-sided triangles. You can already see that there aren’t just by noticing that a four-sided triangle is a contradiction.
[A few years ago, I started two threads on beliefnet where I made these two challenged to anybody who denied logic. I was going to post a link to those threads here, but I can't find them. If I find them, I'll post a link in the comments section.]