My book says "media" is a singular noun, but I think that it is a plural noun. So I should use a verb in the plural form with the word "media".
What is the error in the sentence below?
The media play a vital role in popularising a brand.
I must disagree with Andrew on his claim that in AmE "media" is definitely singular.
Looking at the CoCA corpus "media have" and "media has" have roughly equal counts. I'm not a professional researcher and my ability to use the byu corpora is limited but just going through the results you get examples such as
National media have noticed (Denver News)
the news media have reported (NYtimes)
And the public and the media have the right (spoken CNN)
There is a higher incidence of "media has" it seemed going by a rough look but both versions are certainly present even in AmE.
The oxford dictionaries say:
The word media comes from the Latin plural of medium. The traditional view is that it should therefore be treated as a plural noun in all its senses in English and be used with a plural rather than a singular verb: the media have not followed the reports (rather than ‘has’). In practice, in the sense ‘television, radio, and the press collectively’, it behaves as a collective noun (like staff or clergy, for example), which means that it is now acceptable in standard English for it to take either a singular or a plural verb. The word is also increasingly used in the plural form medias, as if it had a conventional singular form media, especially when referring to different forms of new media, and in the sense ‘the material or form used by an artist’: there were great efforts made by the medias of the involved countriesabout 600 works in all genres and medias were submitted for review.
All in all both plural and singular media is correct in current usage.
The challenge here is that in BrE certain collective nouns are considered plural even when they represent single entities. For example, it is correct (in Britain) to say "the crowd are", but in the U.S. you must say "the crowd is".
Apparently "media" (meaning television, radio, newspapers, etc.) may be either singular or plural in BrE, depending on who you talk to, and also perhaps depending on emphasis. In AmE, "media" is d̶e̶f̶i̶n̶i̶t̶e̶l̶y̶ either plural or singular.
If this sounds confusing, I don't blame you. As a native American English speaker, I don't even try to use plural collective nouns and just stick with what sounds right to me.
Edit: Actually I agree that media can be plural in AmE, but this may be partially due to the fact that it ends in "a" and sounds plural (like "criteria"). Other collective nouns are plural in AmE as well ("the police") but many which are plural in BrE are singular in AmE. As if it wasn't already confusing enough.