Thought does emerge from writing. Something ineffable happens when you write down a thought. You think something you did not know you could or would think and it leads you to another thought almost unbidden.
What is that something ineffable and how do I know this? I do not belong to some kind of occult organization with special séances on the magic of writing, unless you want to so describe, with some reason, the guild of scholars more generally. Everyone who has written at any substantial length, whether prose or poetry, knows that the process of writing itself leads to previously unthought thoughts. Or to be more precise, writing crystallizes previously half-formulated or unformulated thoughts, gives them form, and extends chains of thoughts in new directions.
Lynn Hunt, in a 2010 essay for Perspectives on History, quoted by Nick Heer