There is, of course, a very commonsense way in which biology and physics are talking about things that aren't just texts. But Kuhn helped us realize that understanding the movement of disciplines like physics through history is nearly impossible without actually looking at the interplay of different physical theories, different texts of physics. And then there are all the ways in which Quine, Sellars, and Davidson have helped us see that we cannot just pull off a description from an object, that such-and-such object is partly constituted by its descriptions, i.e. texts.
The recourse to traditions of writing also makes us wary about defining the distinctions between different traditions or genres of writing too squarely. By seeing texts as relationally defined between themselves, we may begin to see new ways of relationally defining them. For instance, Rorty's way of defining philosophy as "talk about Plato, Augustine, Descartes, Kant, Hegel, Frege, Russell . . . and that lot." (CP, 92) Rorty's little list is written in a way to invite us to put in all the great philosophers, all the great intellectuals we traditionally call philosophers. Rorty, however, suggests that such a definition is almost entirely useless to put to use. To get a tradition to mean something a little more, you need to be a little more selective in who you include in the list. (As an exercise, try and get Augustine and Frege to comment on each other.) Not everybody is doing to same thing, commenting on the same line of texts. What's more, sometimes people are doing more than one thing at a time, and so the shape of, say, Kant's texts will change depending on who you place them in relation to. But who you place them in relation to will depend a lot on what you want to do.
Take the example of Rorty's Philosophy and the Mirror of Nature and Susan Neiman's Evil in Modern Thought. Rorty's book delineates a tradition of texts that we might call "epistemology". They are a series of texts that are defined by recourse to a certain problematic and to certain kinds of metaphors, specifically ocular and architectural ones. What Plato, Aristotle, Descartes, Locke, Kant, Russell, Carnap, Ryle, Quine, and Fodor all have in common are a running commentary on the ones before them. And because this sequence looks the way it does, so does the commentary that ends up with Fodor look the way it does. It means that things in Plato and Aristotle that don't hook up with Quine and Fodor are overlooked, not because they are unimportant, but only because they are currently besides the point, they are part of genres outside the one currently being discussed and taken part of.
Rorty's purpose in drawing up that lineage was to cast doubt on the way in which current (early 20th century) Anglophone philosophy was being performed. The three dominant fields of philosophy were philosophy of mind, language, and science. Rorty saw that it wouldn't be enough to simply say that these three subjects were just wrong-headed, or pointless, or boring. He had tell a large story about why these subjects, and not others, arose and took their place at the center of what it meant to be a modern philosopher.
Neiman subtitles her book "An Alternative History of Philosophy". That is very important in seeing what Neiman is up to. She is offering an alternative canon of philosophers in delimiting her subject matter, in seeing what modern philosophy is up to. Instead of Rorty's "Plato to Fodor" canon we get "Leibniz, Bayle, Rousseau, Kant, Sade, Schopenhauer, Nietzsche, Freud, Camus, Arendt". Kant is in both canons, but he almost looks like entirely two different philosophers in the two books because of the different relations of texts Rorty and Neiman put him in. Neiman says in her introduction that
the picture of modern philosophy as centered in epistemology and driven by the desire to ground our representations is so tenacious that some philosophers are prepared to bite the bullet and declare the effort simply wasted. Rorty, for example, finds it easier to reject modern philosophy altogether than to reject the standard accounts of its history. His narrative is more polemical than most, but it's a polemical version of the story told in most philosophy departments in the second half of the twentieth century. (6)
I think Neiman is being a little unfair to Rorty, but I can forgive her because she's essentially right, not that Rorty rejects modern philosophy, but that he's recounting the standard story that most anglophone philosophers tell themselves. He recounts it the way he does specifically to show them that it doesn't end well for them. What Rorty, by his own admission, hasn't done entirely well (or at least as well as some others) is tell an alternative story of philosophy that gives philosophers something else to do. I think it's unfair to criticize Rorty on this point, of not offering an alternative account, for the same reason it would be unfair to criticize the forensic body specialist on (insert your favorite cop show here) for not single-handedly capturing the perpetrator. He played his part, not everybody is suited to do everything. We in fact can catch Neiman at cross-purposes with Rorty by turning over the book to the back cover where, for the 2004 paperback release, we see Rorty adding his praise to other luminaries as Jonathan Ree and Michael Walzer (2004 edition) and Clifford Geertz and Jerome Schneewind (2002 edition): "We badly need alternative histories of philosophy. The story told (by me, among others) cries out for supplementation.... Neiman's snazzy prose makes this book a pleasure to read, as well as an immensely welcome change from the sort of history of philosophy to which we Anglophones have become accustomed."
My point in this detour in examples is about the fluid nature of philosophy, let alone the wider panorama of "the written word." Not all contexts produce something interesting, but putting books into strange relations to other books can sometimes create something fruitful. Not all pieces of writing implicitly comment on Plato, but most produce something we might call wisdom and so can be placed in other traditions of wisdom literature, philosophy, traditions that we can create by situating the books together. All that is needed is a context and a persuasive reason for creating the context, some interesting insight produced by the pattern of texts placed beside each other. Genres of writing are created and all texts sit implicitly aside other texts and sometimes the mere act of writing can create a new genre, a new tradition of commentary.