‘Agreement’ is the term for words grammatically matching each other.

Forms of agreement include verbs agreeing with their subject, and pronouns agreeing with nouns or noun phrases they refer back to (known as the antecedent).

Verbs must agree with their subject
Verbs must be singular or plural depending on the subject. This is not usually a problem unless the verb gets too far away from its subject and we relate the verb to another noun.

The contract is ready. The contracts are ready. (Obvious!)
The number of accidents caused by young people increase after they have been drinking or smoking dope. (The verb should be increases.)

Pronouns must agree with their antecedents
Pronouns must agree with the nouns or noun phrases they refer back to. The noun or noun phrase referred back to is known as the antecedent.

Several people protested. They were concerned about the issue. (people = antecedent)

This causes a problem if the lack of agreement causes ambiguity. Who is doing the dumping in this paragraph – the banks or the hedge funds?

For example, the conversion of former US investment banking giants Goldman Sachs and Morgan Stanley into commercial banks (which have tougher capital requirements) had the unintended consequence of squeezing funding to hedge funds – which in turn has exacerbated their dumping of assets across world markets. (Australian Financial Review)

Company names and other collective nouns

The most common inconsistency in business writing is company names. Which would you say?

The bank is raising its interest rates.
The bank are raising their interest rates.

The Australian Commonwealth style manual says:

While either singular or plural agreement is grammatically correct, the singular is recommended in Commonwealth publications – both for consistency, and to present a cohesive image in references to government bodies and activities. (p71)

Treat all company and organisation names, not just government bodies, as singular. This applies to Australia and New Zealand. Other countries may take a different approach.

However, when you use a pronoun to replace the company name, it is now regarded as acceptable to switch to the plural. If this looks clumsy, consider changing your wording.

The company is hiring new people. They are looking for people with accounting experience.
The company is hiring new people. Accounting experience is necessary for the roles.

Other collective nouns
Some other collective nouns that describe a group are jury, team, family, staff and management. These words can take either the singular or plural verb depending on the context.

The staff is united on this issue.
The staff are giving each other presents this Christmas.

To avoid inconsistencies, you can change the wording.

Staff members are giving each other presents this Christmas.

Indefinite pronouns

Indefinite pronouns can be troublesome. Indefinite pronouns refer to unspecified people, things or groups.

all, some, none, anyone, everyone, many, some, several

Some indefinite pronouns are always singular, while others are singular or plural depending on the context.

all and some
Some indefinite pronouns, such as all and some, can be either singular or plural.

Some of the directors are still waiting for their papers.
Some of the milk has turned rancid.

anyone, everyone, no-one, someone
Indefinite pronouns ending in -one, -body or -thing are always singular.

anyone, anybody, anything
everyone, everybody, everything
no-one, nobody, nothing
someone, somebody, something

Has anybody seen my ring?
Someone has stolen my ring.

It is now acceptable to follow a singular indefinite pronoun with what is known as the ‘singular they’.

No-one could find their ticket.

each, every, either, neither
Each, every, either, neither are singular and take a singular verb.

Every person in the room is wearing a red scarf.
Neither of them is coming.

However, in informal speaking and writing, neither and either sometimes take a plural verb when they are followed by of.

Have either of you seen my glasses?
Has either of you seen my glasses?

When the construction is either/or or neither/nor, the rule is that the verb agrees with the closest subject.

Either the secretaries or the manager decides the menu.

You should not use either/or or neither/nor to separate more than two items.

none
Most grammar experts agree these days that none can be singular or plural. It usually doesn’t matter whether you choose a singular or plural verb, unless something else in the sentence dictates your choice. Either of the following sentences is OK.

None of you are guilty.
None of you is guilty.

In the following sentences, other words determine the agreement.

None of their clothes were dry.
None of the beer was drunk.

not only… but also
The correlative pronouns, not only/but also, can be used to make a strong statement. To work effectively, the syntax of the two points must be the same and the two items linked must be similar in kind.

Clive James not only wrote non-fiction but also poetry. (wrong)
Clive James wrote not only non-fiction but also poetry. (correct)

This includes not only the activities, but also captures the data. (wrong)
This includes not only the activities, but also the data. (correct)

one or more, one in, one out of and one of these
Which of the following sentences do you prefer?

One or more of the workers is covered by the scheme.
One or more of the workers are covered by the scheme.

I would choose the plural, but some grammar experts think one or more, one in, one out of and one of these should always take a singular verb.

The argument for the singular is that one is singular. The argument for plural is that the people or things being referred to are plural.

Compound subjects

A compound subject joined by and takes a plural verb.

John and Alison are coming for dinner.

Phrases such as together with, as well as and along with do not have compound subjects so they take a singular verb.

The manager as well as her deputy is at the meeting.
The manager and her deputy are at the meeting. (compound subject)

Some items have become joined by convention and are treated as singular.

Bacon and eggs is my favourite meal.

Fractional expressions

Fractional expressions, such as half of, majority of and a percentage of, are singular or plural depending on the context.

The majority of the crowd was unhurt.
A large majority of the voters were angry.
A quarter of the wine was too old to drink.