Thinking again of the short essay by German writer Heinrich von Kleist written in 1805, "Über die allmähliche Verfertigung der Gedanken beim Reden" : "On the Gradual Construction of Thoughts While Speaking".
His argument is that speech doesn't express a thought that already exists; it produces the thought. You begin to speak before you know what you're going to say, and the very act of speaking, especially to another person, even an inattentive one, creates the conditions for the idea to emerge and clarify itself. for von Kleist, we think by speaking. The act of beginning to articulate something to another person, before the idea is fully formed, creates a momentum that carries thought forward to a clarity it could never reach in silence. The other person's presence is essential not because they contribute anything, but because the social obligation to continue forces the mind to finish what it started.
I think of this often when I am doing public speaking or teaching and I have not prepared a full script (sometimes because I have little time to prepare or just procrastination). And it always amazes me how just talking out loud to someone about it helps me clarify and formulate my thoughts. It is one of the reasons why I like talking about my works in progress. I see the thoughts form in real time and even I am amazed by how just speaking helps me in this regard.