Meaning of "discursively"

I've been reading a book called "Rhetoric of the Unreal" by
Christine-Brooke-Rose, which is about literary criticism of genres
called "fantastial". 

In it she says, of the Canadian critic Northrop Frye:

"He presents five modes, one after the other, selecting categories for
each, discursively and of course very persuasively."

For me the "of course" strikes a jarring note. 

If something is discursive (rambling, wandering around in an
unsystematic manner and never getting to the point) it is hard to see
it as being persuasive at all, never mind "of course".

Does "discursively" have a special meaning in litcrit speak tha is
other than the norrmal everyday meaning of the word, and if so, what
is it? Can anyone explain? 

A DuckDuckGo search doesn't help. 


-- 
Steve Hayes from Tshwane, South Africa
Web:  http://www.khanya.org.za/stevesig.htm
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