Corporation speaks to not just any capital, but to capital concentrated in the hands of huge business enterprises. The organizational dimension is not trivial.
'Corporations' are about sociology and the practical economics of industrial organization. Capital is more abstract. Not exactly opposing concepts.
I might also note -- in fact I definitely will -- that the empirical study of corporations reveals controlling motives other than profit maximization, a shortcoming in Marx that dovetails with his focus on "capital."
mbs
You've got to watch these folks that talk about "the corporation" rather than "capital." But Barber won't talk about capital, since to do so would be to participate in "the arid debate about capitalism and socialism."
Doug