Kind of both at the same time. I "feel" what I'm writing. It's like thinking but with feelings. and then I just let it flow.
It depends what I'm writing. Random thoughts I scribble down in journals or notebooks I don't always put much thought into. When I'm actually trying to write a philosophical piece I'll usually put more time into considering what I want to explain or question.
Hmmm, is something hard to explain. For example, it depends in what I am writting at the moment. I mean, if I have something in mind, generally, I do 50% and 50%. I know what I should write, and, more or less thanks what I have in head, I write it as I let it flow. And, if I feel something doesn't fits, I take it out.
On the other hand, sometimes, I don't know what I am going to write, and I totally let it flow. Mostly, I like what I write in this way. I feel that it is the deep shit I have inside, and that expresses what I want to and what I feel in the moment.