Well then, before we even get to tense, which you seem stuck on, you also have to look at the meaning of the words used. You say there's nothing wrong with the statement "I'm definitely right, but then again, I could be wrong." How so? If you're "definitely" right, then that means you are confident that you are right. It makes no assumption as to when you are right, only that you ARE right. And if you're definitely right, then you can't also be wrong, at any point, when talking about the same thing. Can you say "the ocean is definitely wet, but then again, it could be dry"? No, b/c it can't be both at the same time, and you've already said that it is DEFINITELY wet. You can't use an "absolute word", in whatever tense, and then contradict that absolute word. It IS absolutely incompatible.