Jay Garfield's systematic exposition of Nāgārjuna's Mūlamadhyamakakārikā is my most referenced source for interpreting Mādhyamikan Buddhism but I have found the work of Robert Magliola valuable too. In particular, Magliola's interpretation highlights the differential mysticism of Mādhyamika in opposition to the more popular strand of centric mysticism which often characterises Buddhism and older Hindu thought, such as the philosophy of the Upanishads. Central to differential mysticism is the characterisation of reality as an implacable process of alterity. It is through this alterity that any candidate for identity is thoroughly negated. This, Magliola states, is in stark contrast to the self-identity implied by the undifferentiated center one finds in centric mysticism. Citing Frederick Streng, Magliola begins to make this contrast clear in Derrida on the Mend:
"A major difference between Nāgārjuna's negative dialectic and the Upanishadic analogic use of words, however, is that unlike the 'Neti, Neti' (not [this], not [that]) expression in the Upanishads there is no inexpressible essential substratum which the negations attempt to describe. For Nāgārjuna, in place of the Brahman-Atman is anātman (no individual identity). The purpose of Nāgārjuna's negations is not to describe via negativa an absolute which cannot be expressed, but to deny the illusion that such a self-existent reality exists." Nāgārjuna "is not saying that the true eternal state of reality is a blank; the calmness of nirvāna does not refer to an ontological stratum beneath or behind the flux of experienced existence."
(Streng, cited in Magliola, Derrida on the Mend, p93-94)
He also elaborates on the origins and rise of the ultimate self-identity implicit in centric mysticism, its adoption by some schools of Zen Buddhism, and its subsequent dominance of Western perceptions of mysticism. It is an interesting section on Buddhism's history which I may return to but here I will refer only to its concluding comments which I think are important as they serve to accentuate a conception of reality that could easily be mistaken for Nāgārjuna's position but which is, in fact, rejected.
Westerners, through the good offices of Zen's great missionary to the West, D.T. Suzuki, know only of logocentric (and thus absolutist) Zen, and indeed there is no question that logocentric Zen has been for quite some time now Zen's most popular form. Or, to avoid needless confusion, let us call it "centric Zen," since its whole effort is to transcend logos understood as the language of is and is not and to achieve the 'undifferentiated center'. Thus Suzuki declares that "The meaning of the proposition 'A is A' is realized only when 'A is not-A'," that Buddhist philosophy is the "philosophy of self-identity," and that in this self-identity "there are no contradictions whatsoever." The supreme self-identity, indeed the only self-identity in the ultimate sense, is centric Zen's śūnyatā: "Emptiness is not a vacancy - it holds in it infinite rays of light and swallows all the multiplicities there are in this world."
(ibid., p97)
So, the point being made here is that, in the differential mysticism of Mādhyamika, śūnyatā, i.e., emptiness, is not an Upanishadic substratum nor a frame in which the entire multiplicity of phenomena is contained, or held, as it is in the 'absolutised Zen' described above. Instead, recalling from an earlier post that emptiness is dependent arising, it is characterised as a process of ongoing, ever-altering dependency and is thus always other than what is framed by any fixed term of reference or singular gnostic experience, hence the significance of the term 'alterity'. Therefore, the idea of enlightenment as a centering of awareness upon an immutable reality is untenable to the differential mystic. Rather, as Misra, cited in Derrida on the Mend, puts it:
[E]nlightenment itself is reality, in my view, not anything about which one is enlightened. And this is, according to me, the basic distinction between the Vedanta and the Mādhyamika: that in Vedanta enlightenment is enlightenment of Brahman, the awareness of Brahman as the Absolute, and in Mādhyamika enlightenment, or prajñā, does not mean the awareness of any reality. It means the awareness that things are essenceless or śūnya (empty of essence)....and this is freedom.
(ibid., p95)