Confounding of collective noun and mass noun

There is often confusion about, and confounding of, the two different concepts of collective noun and mass noun. Generally, collective nouns are not mass (non-count) nouns, but rather are a special subset of count nouns. However, the term "collective noun" is often used to mean "mass noun" (even in some dictionaries), because users confound two different kinds of verb number invariability: (a) that seen with mass nouns such as "water" or "furniture", with which only singular verb forms are used because the constituent matter is grammatically nondiscrete (although it may ["water"] or may not ["furniture"] be etically nondiscrete); and (b) that seen with collective nouns, which is the result of the metonymical shift, discussed earlier, between the group and its (both grammatically and etically) discrete constituents.

Some words, including "mathematics" and "physics", have developed true mass-noun senses despite having grown from count-noun roots.