Count nouns refer to objects, while mass nouns refer to substances. An object is a
sharply delineated entity, and if it is divided into smaller pieces, these pieces are no
longer instances of the same object (a horse cut in two does not give two horses). A
substance is not sharply delineated, and if it is divided into smaller pieces, these
pieces are instances of the same substance (smoke remains smoke even if divided in
two). This distinction plays a central role in the grammar of English, as it does in
Swahili and many other languages of the world.2
In Japanese, the distinction between count nouns and mass nouns is
grammatically unimportant, for the following reasons: