English in Use/Subject-verb Agreement

English features a loose conjugation and declension pattern. For this reason, subject-verb agreement is of paramount importance.

Subject-Verb agreement is a rule which states that the number present in a noun must agree with the number shown in the conjugated form of the verb that is being used, and that the person of the noun must agree with the person of the conjugated form of the verb that you are using.

Proper Subject-Verb agreement:

TO BE: I am - you are - he is - we are - you are - they are
TO WORK: I work - you work - he works - we work - you work - they work

Where the subject is a pronoun or complex or modified as part of an adjectival phrase, or modified by parenthetic expressions, or clarified in meaning by common knowledge or something that occurs later in the sentence, then subject-verb agreement can become a little more complicated. Some grammar rules say that the complex part of the subject closest to verb in the sentence should determine the verbal agreement. However, many examples can be found that make this sound funny. A better rule is to consider the entire complex subject phrase as one subject, and then think about what kind of thing it represents.

The basic idea in idiomatic English is to make the verb agree with the idea that the subject REPRESENTS, which could have different plurality than the actual subject as a word. This is actually helpful in understanding meaning since it gives subject-verb agreement a role that is not simply redundant (in echoing the pluarity of the subject). Whatever the subject represents can be considered singular or plural, and that is what the verb should agree with.

The president and the children (plural) are at the party.
Neither the president nor the children (plural) are at the party.
Either the president or the children (plural) are at the party.
Neither the children nor the president (singular) is at the party.
Somebody (singular) is at the party.
Nobody (singular) is at the party.
We (plural 1st person) are at the party.
I (singular 1st person) am at the party.
The Three Musketeers (singular-book) is a good book.
Ten dollars (singular) is enough to buy the book.
Ten dollars (plural) are in my pocket.
Economics (singular subject of study) is an interesting subject.
Bryans and Hastings (singular supermarket) is a great place to shop.
The idea of serving frankfurters (singular idea) is a good one.
My sister is (singular) with my friend, Roberta, at the party.
My sister and my friend are (both) at the party.

In many cases, the author decides whether the subject represents something singular or plural, depending upon which idea is desired to be expressed. For example, a group can act as a whole (singular) or as a group of individuals (plural), and despite many attempts at making rules for this, there is no simple rule that covers all cases:

All of my family is going camping.
Most of my family is at the party.
All of my family are fans.
Some of my family are fans.
Most of my family is at the party.
Most of my family are at the party.
Some of my family are in their homes.
The sounds the car makes, the ways they irritate (singular idea stated with 2 phrases)--it is all the same idea no matter how you say it.

Another needed example is one in which the noun that is clearly singular until the entire sentence is read, and something near the end changes the meaning of the noun so that it clearly represents a plural thing.