Can you speak without knowing what you're about to say beforehand? (I'm pretty sure I can't.)

I can, though when I do, it's often consists of regurgitating bits and peices from long mental monlogues that I had in the past, with a bit of new content thrown in to make things flow better (specifically, the one where I articulated my experience with pre-thinking what I'm going to say years in advance occured nearly four years ago, in my senior year of high school, while sitting in a Spanish Class).