 Addressing issues surrounding abstract, psychological, and quantitative mass nouns and their referents is beyond the scope of this  article.[12]  Due to the almost exclusive emphasis on concrete and quasi-concrete mass nouns in the metaphysics literature, this article will follow suit. While an analysis of concrete and quasi-concrete mass expressions could possibly be carried over to generate a general metaphysical theory of masses, the prospects for this are dim. This is because, even given the grammatical similarities between all mass expressions, there are far too many differences between concrete stuff and the entities in categories  (c)–(e).[13]