Perelman's arguments remind me a lot of Thomas Kuhn (summarized on page 1196 in the overview of modern and postmodern rhetoric). Kuhn challenged the binary between communal argument and science, which seems to also be what Perelman is doing.

I was surprised by this distinction; I tend to think of science as dealing with the concrete and rhetoric as dealing more often with the abstract. I wonder if Weaver's distinction was more common in his time than now.