Material Causality, Writing, Experience

It seems that it would be difficult for an author to deny that "I am writing this". Thus, a book that seeks a self-evidently true foundation of a theory of Experience could begin with an examination of the process of Writing. The study might proceed to analyze that Writing is a physiological act of its author's self-expression, appearing in an extensive medium, developing ideas to be communicated to others. It could, accordingly, infer that self-extension is a fundamental dimension of Experience, in general, and, since, self-extension is a type of self-variation, that Material Causality is an essential component of Experience. It would also expose as paradoxical, if not absurd, books that articulate the thesis that philosophizing is a private, incorporeal endeavor, especially where they attempt to argue that the existence of Extension is dubitable.