'mass' mix-up

0Hi,02br
02br
00I am in a situation where I am having a bout of 'mass nouns' mix-ups and I am going to ask a mixed bag of questions all related to mass noun usage.02br
02br
00In a thread named 'a soap' started by Vincent Teo, Mr. M. noted that he should use 'soap' instead of 'a soap'.02br
02br
00I think Vincent used this sentence:02br
02br
00She washed her hands with a soap/soap.02br
02br
00When you walked into premises where security is important, you wll likely to encounter signs like "No liquids allowed' and you will know what that means: No various kinds of liquiid substances are allowed.02br
02br
00I think the words 'soap' and 'liquid' are mass nouns and that seems to mean you can use it to refer to a substance, I think that is what we see it used in in most of normal writing situations, and use it to refer to types and brands. I think in reference to the sign, I am sure I have made the latter reference in my use. To me, when you can use a noun in its pluralistic sense, it seems to be logical to construe that you can use it in its single-component sense -- if that sense exists at all: for example, 'liquids' is OK, then, 'soaps' should be OK too.02br
02br
00 Why is that I see expressions like "I need more detergents (which seems to be another mass noun)" and don't see much of "I need more soaps"? 02br
02br
00Why is that I seem to see many expressions like "I need different detergents" and don't see much of "I need different detergent" when I think "different detergent" and "different detergents" are grammatical phrases, based on my knowledge? 0-