 In contrast, if the quantity is not accidental to the void but is essential to it, then void would be a species of quantity. Avicenna now challenges the defenders of void to provide some positive difference that would make up void’s species. It cannot be that void is a material quantity, since again a material quantity is body. If one claims that void is immaterial quantity, Avicenna demands some non-negative difference, for while there are immaterial substances, like angels, one can provide a positive characterization of them as intellectual substances. Avicenna offers a number of suggestions, but finds every attempt wanting or ultimately telling us what void is not rather than what it is. Since no definition of void can be given in terms of a positive genus and difference, Avicenna concludes that our idea of void is nothing but empty imaginings. 