Freeguy posted:Practical English Usage, Michael Swan, Page 520:
Many singular quantifying expressions can be used with plural nouns and pronouns; plural verbs are normally used in this case:
- A group of us are going to take a boat through the French canals.
What's the difference, then?
Hello again, Freeguy,
The difference is that, in sentences like the one you asked about, "a group of X" picks out a specific individual group with specific members (like "p-r-e").
"A group of us are going" is simply talking about a plurality of people that includes the speaker. It's like saying "A bunch of bananas are in the refrigerator."
In place of "a group of letters," in the sentence you originally asked about, you could use the phrase "a letter group," which is more obviously singular.
- A prefix is a letter or a letter group that comes at the beginning of a word.