grammar - Is "group" singular or plural?

When I'm referring to a group of multiple things, should it be considered singular or plural for the purposes of applying a verb to it? For example, which is correct in the examples below?

A sentence is a group of words that is followed by a period.
A sentence is a group of words that are followed by a period.

The group of people constitutes a jury.
The group of people constitute a jury.

A group of crows is called a 'murder'.
A group of crows are called a 'murder'.

My instinct is that it depends on whether the verb is referncing the group itself or the members of the group directly, but is that right?

Answer

According to the OALD, group can actually serve as either a plural or singular noun. The category they give is "countable + singular or plural verb". So, an example of correct use is:

A group of us is/are going to the theatre this evening.

For any of your examples, both is and are can be used. I think the difference between them is as you say: use is when you are referring to the group, and use are when you are referring to the members of a given group. This page on when to use "group" as plural from Washington State University backs this up, saying:

When the group is being considered as a whole, it can be treated as a single entity: “the group was ready to go on stage.” But when the individuality of its members is being emphasized, “group” is plural: “the group were in disagreement about where to go for dinner.”

To analyze your given examples, here are some notes:

• A sentence is a group of words that is followed by a period. Use this form if you're talking about the group itself. That is, a sentence is a group of words followed by a period.


• A sentence is a group of words that are followed by a period. This implies that "This. Is. A. Sentence" is a sentence.


• The group of people constitutes a jury.


• The group of people constitute a jury. This would be more correct, since you are describing the nature of the group.


• A group of crows is called a 'murder'. This would be correct, since you're again describing an entire group.


• A group of crows are called a 'murder'.