Let us begin with some examples of collective nouns.
a crowd
a range of mountains
a deck of cards
a pile of books
an anthology of poems
a bunch of grapes
a pack of wolves
a swarm of bees
a network of computers
a host of golden daffodils
The words in italics in the above phrases are collective nouns.
What Are Collective Nouns?
They are names of collections. They are not the names of the individuals in a collection. The collections may be of...
people (crowd, orchestra)
animals or other living things (herd, swarm)
places (union, federation) or
things (bunch, pile).
Some Possible Points of Misunderstanding:
Usually examples for collective nouns are given in a phrase form: a bunch of grapes, a swarm of bees, etc. Please know that the words bunch and swarm are collective nouns; the words grapes and bees are not.
A collection should not be confused with the plural of the elements in it. The plural of a grape is grapes. Neither of the two words is the name of a collection. The name of the collection is bunch. Therefore, bunch is a collective noun, not grapes.
A mass noun (uncountable noun) is not the same as a collective noun. A mass noun is something we think of as complete and cannot have a plural. A collective noun has a plural - crowds, ranges, decks, bunches.
Are Collective Nouns Singular or Plural?
Observe these two sentences:
The staff works for four hours on Saturdays.
The staff are unhappy with the decision to make them work on Saturdays.
You will notice...
that the word staff in sentence 1 is singular. We know this from the verb which matches it (works is singular).
The word staff in sentence 2 is plural. The verb are shows us this.
How can the same word be singular at one time and plural some other time? Why is the word staff used like this?
The British System:
In sentence 1 above, the staff is thought of as one collection. In sentence 2, we are thinking of the staff as a number of human beings who are unhappy. This is very true to human ways of thinking, even though it does not seem logical. (But human life has its own deeper logic which we cannot always hold within the rules of the science of logic.)
This is the British English tradition which we in India have been following and which I learnt as a child. You may need to sense what is being emphasized in a particular context whether the particular collective noun is looked upon as a whole or as parts put together.
The American System:
But here is a no-complication system. This is obviously logical (i.e. according to rules of logic). In this system, the above sentences are rewritten as follows:
The staff works for four hours on Saturdays. (no change)
The members of the staff are unhappy with the decision to make them work on Saturdays.
When you write the sentences in this way, the collective noun staff is singular since it is a single collection of people. In sentence 2, members is a plural word for the number of individuals within the collection. This is the preference of American English. I prefer this second approach when teaching my students about collective nouns.