The assumption of the self-possession of the text is more than time honored. In some sense the assumption is correct. Philosophy is the discourse that refuses to accept a meta-discourse above it. The discipline that acknowledges no limits other than those it discusses. (Derrida--as well as Kierkegaard and Nietzsche and Heidegger and Wittgenstein, among others--is right to point out that there may be limits it cannot discuss.) But for what it can discuss, to discuss means already to be beyond the limits, as Hegel pointed out. Deconstruction and its cousins are very close to Hegel in the awareness that the conditions of possibility of discourse are subject to themselves and are only known in motion, living on the borders. (Of course they differ from Hegel on the self-coincidence of that motion, and what it means to live on the borders, which is just the issue at stake here.) And notice that Derrida also insists that you cannot just walk over those borders into a new world.