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Here we come to the very heart of Mahayana Buddhism and of Zen-the doctrine of prajna, particularly as it appears in Hui-Neng and his followers. The Void which is the topic of this book, this Emptiness or Nothing which stands so magnificently alone, is certainly no mere Void, no common Emptiness, no negligible Nothingness: for it is conscious of itself as Void and Empty and Nothing. (This very statement is sufficient evidence of the fact!) It is not only the Self-producing source and destroyer of all the world's richness, a fountain gushing infinite energies, and moreover the knower of Itself in these capacities; It is also the knower of Itself as at once absolutely knowable and unknowable, and neither of these-as absolutely free of all such complications.

Preface by Richard Lang available here.