The monad / dyad thing actually goes pretty far back to Ancient Greek philosophy. As for Balthasar's usage of it, it has to do with "the two roles of woman," ie. as both bride and mother. She is seen as the "answer" to man, the principle which supposedly completes him, as well as the source in terms of birth as a creative capacity. Balthasar uses the concept of "ossiclation" to try and argue that woman is both equal to man insofar as she too is human, yet subordinent to him at the same time due to her dyadic nature. Apparently man as monad has an inner unity and thus does not experience this ossiclate, has no comparable experience with which to relate to woman.
For Balthasar, receptivity, yielding, and obedience are distinctly feminine qualities whereas leadership and representation are masculine. That sort of goes back to the Church being seen as "the bride of Christ" in its obedience and receptivity to the Word.
Of course, one wonders how Balthasar can conveniently ignore the dual role of man as father and bridegroom, which would make him of a dyadic nature as well.
Edited by MuppetFace - 9/15/12 at 4:25pm