He did the same thing with "philology" that he did with "rhetoric." It's just the bald assertion that he's doing the same thing you're doing, except he doesn't want to put in the time learning specialized methods or doing the empirical grunt work (sustained effort, especially in de Man's case, not being the hallmark of the deconstructionists).
Philologists analyzed the evolution of words to study the structure of language; de Man mentioned words and noticed that language has structure; hey, they're doing the same thing so he must be a philologist too!
It's like summer camp. You get to be whatever you want to be. He pulled the same nonsense with rhetoric. Rhetoricians analyze tropes to understand how language becomes persuasive; de Man mentioned tropes and noted that language is persuasive; hey, they're doing the same thing so he must be a rhetorician too!
You'd think he's just trying to hijack the ethos of philology for whatever hand-waving he's engaged in, and you'd be mostly right. But there's also a more pernicious move, which becomes more noticeable when it's applied to scientific rather than humanistic disciplines (though it's applied by this crowd to both). It's the same double-move every time: "rigorous methods don't have any privileged access to knowledge" (the you're-not-doing-anything-special move) and "postmodern methods are just as rigorous as any other methods" (the what-we're-doing-is-just-as-special-as-what-you're doing move).
Or more tersely, now that I've read his philology essay: "hey, philologists think about language; I Paul de Man think about language; I'm doing philology too!"
The move requires a strange combination, driven by a con man's confidence but insulated by ignorance.
If we take some uncontroversial 30,000ft view of knowledge — disciplines split off when particular methodologies align nicely with particular objects of study, so that we can squeeze out new insights — then you can see how total ignorance of specialized methodologies would help. If you don't actually know what someone is doing, you can say with confidence you're doing the same things they are. So Lacanians who can't do math or logic claim they're doing analytical philosophy. Literary scholars who have not the foggiest clue about phonology or morphology are doing philology. And per Richard Rorty, we're all doing science, because after all that's just a narrative too.
There's an anti-intellectual version of this conceit, which is buoyed by the kind of journalism that insists experts ain't all that smart anyways. There's a version found in the workaday academy, which is usually cashed out as complaints about boundary policing. But if you're a former Nazi sympathizer with a European accent taking in the rarefied air of the 1960s humanities, it goes all the way to being the height of sophistication.
I'll add another perhaps-relevant factor: the supreme intellectual prestige of "philology" in Europe through the middle of the 19th century, and to some extent until WW I. Thus de Man implicitly positions post-modernism as a return to pre-modern verities. The publisher's blurb for James Turner, Philology: The Forgotten Origins of the Modern Humanities(2014) explains:
Many today do not recognize the word, but "philology" was for centuries nearly synonymous with humanistic intellectual life, encompassing not only the study of Greek and Roman literature and the Bible but also all other studies of language and literature, as well as religion, history, culture, art, archaeology, and more. In short, philology was the queen of the human sciences. How did it become little more than an archaic word? In Philology, the first history of Western humanistic learning as a connected whole ever published in English, James Turner tells the fascinating, forgotten story of how the study of languages and texts led to the modern humanities and the modern university.
To begin with, when people ask me what my profession is, I've always replied that I am a Sinologist, but most people don't know what a Sinologist is, so that leads to complications.
Let me illustrate.
The first book that I published with a commercial press was Tao Te Ching: The Classic Book of Integrity and the Way (New York: Bantam, 1990), a translation of the Literary Sinitic text, with extensive commentary and notes. My editor asked me how I wished to identify myself, and I told her that I was a "Sinologist". She said, "That won't do, because nobody knows what a Sinologist is. Can't you call yourself a linguist?" I told her "That won't do either, because I'm not a linguist."
I do not consider myself a linguist (e.e., historical linguist, phonologist, etc.) per se, though I certainly do dabble in these things quite a lot, but truly am a Sinologist, and have been since I began graduate school. Yet it's not only in commercial publishing that I can't call myself a Sinologist, in current academia it's not fashionable to refer to oneself as a Sinologist either, so I am formally designated as "Professor of Chinese Language and Literature at the University of Pennsylvania".
If I have time and opportunity to go into more detail, I still will always style myself as a Sinologist. When people look at me and say, "Huh, what's that?", I reply that a Sinologist is a philologist who specializes on matters pertaining to China. To which they will generally ask, "Huh, what's that?" Whereupon I will say, "A philologist is someone who studies ancient texts for the purpose of understanding the languages and cultures of the times in which they were written."
I definitely think of myself as a philologist specializing in Sinology. Disciplines parallel to Sinology are Indology, Japanology, Semitology, and so forth. For the majority of scholars, these have now morphed into Indian Studies, Japanese Studies, Semitic Studies, and so on, but I'm old fashioned and still cling to the old ideals and old methods of Sinology, though happily assisted now by modern technology and techniques (computers, data bases, online resources, etc.). There is, however, clearly an effort on the part of many to get Beyond Sinology (title of a brand new book by Andrea Bachner, with the subtitle Chinese Writing and the Scripts of Culture), by which they usually prescribe the approaches of individuals like Paul de Man (born as Paul Adolph Michel Deman), Jacques Derrida, Michel Foucault, Pierre Bourdieu, Louis Althusser, Stanley Fish (though he sometimes gets serious about textual and historical studies), Fredric Jameson…. (the list is very long).
My views on all of this are spelled out in a lecture entitled "Sinology then and now: Methods and Aims", which I delivered at Peking University, June 7, 2012, available here and here, but it's two hours long, so don't start watching it unless you have a leisurely morning, afternoon, or evening with nothing else to do.
In closing, I would like to declare, as I have on many occasions, that although I do not consider myself a pucka linguist, I deem it a very great honor to write for Language Log, where everyone else is a real linguist.
Day after party report -- I wake to find that Kevin has done all the remaining dishes. I have found my prince charming. Plan for the morning: straighten up, moving slowly, while watching some more episodes of The Good Wife. Feed children as required: leftover scones seems like a perfectly reasonable breakfast food. There are some summer bulbs that must get into the ground today, dahlias and lilies and what not. Friends are having an open house from 11 - 4, so I think we can stumble over there at some point and let them feed us. At some point today, must prepare a stellar lesson plan for tomorrow, as I am being observed in class; it's a little unfortunate that it's a book I haven't taught before, but so be it. If anyone has some fabulous ideas on starting to teach The Handmaid's Tale, please pass them along. And that's Sunday.