Get in touch with potential advisors, although I have no clue what my topic might be? I am in the Humanities, and I have a rough idea about the general field I want to work in. I have identified several professors who also work in this field. However, I am not sure how I can now find a topic for my dissertation. I am reading and reading, but as of now, I do not have a great idea. 

I was thinking of getting in touch with the professors who might be potential advisors, but I am not sure whether that's a good idea considering I do not know my topic at all. I do not want to come across as naive - esp. since they are all at prestigious institutions.

If you think it is a good idea to get in touch, then I am still clueless about how to go about this, and what to write. I want to be honest but would like to avoid looking like a fool.

PS: I am in the Humanities, I think it's important for this question.
I don't think it is a good idea to contact them for several reasons. First, by your own admission, you do not know what you wish to focus on. Bear in mind your competitors probably already have a specific research question in hand. Second, even if you do have a research question at hand, academics in social sciences/humanities generally do not respond (of course, I can't speak for everyone) to potential candidates' emails prior to their official submission or consideration. That is to say, your prior email, in theory, has no effect on whether the professor would positively view your application that way.