Ignoring the difference in spelling between "mould" and "mold" for the moment, I need to categorise the following terms into "masses of substances" or "masses of substances made up of parts too numerous to count". The two contentious items are "mould" (as in fungi) and "mud".
Under "masses of substances" we have glue, margarine, tofu, beer. Under "masses of substances made up of parts too numerous to count" we have gravel, dust, sand, flour.
Where should mould and mud go?
I'm editing a grammar text book. This is one of the practice exercises, and I'm busy with the answer book. Unfortunately the author and I can't agree on mud and mould, and the author doesn't seem so sure. The instructions are: "Draw a table, write the nouns from the list under the correct headings".
Usage is not at stake here because it is the same. We're trying to highlight the conceptual difference between a substance made up of parts which theoretically one could count and something that is a mass. We need to differentiate between these two types of substances so that students can recognise that sand and gravel are uncountable, even though they are made up of countable particles. We also do not say "many waters" but that's easy for the average student, there is no way to count units of water.