I was puzzled not to find any mention of "emptiness" (as expounded upon by Nagarjuna and Chadrakirti, not the feeling one blogger has when his relationships end.) Is that not an issue that our learned philosophical crowd seriously contemplates these days?
I have to say I think about nothing all the time, both in the sense of not thinking about anything, and in the sense of contemplating the concept nothing . P.L. Heath has a very fine piece on "Nothing" in the Encyclopedia of Philosophy . On the other hand I suspect that śūnyatā is not really emptiness or literally nothing - śūnyatā is a kind of non-substantiality, certainly, but in Western metaphysics that does not mean a non-entity. The point is that śūnyatā is emptiness, but of the detritus of external influence, or void or outside dependence. It has its own quality. It is also like a kind of expectant fulness, empty as the rich expectation of a joyous future event is in an obvious sense empty (of the event) compared with the experience of the event itself. A quality however is an entity, though not a substance.