Agreement with the noun in number, gender and person
A personal pronoun must be of the same number, gender and person as the noun it stands for.

• John is a bright student. He won a prize in science.

Here the personal pronoun ‘he’ is of the same number, gender and person as the noun John.

More example sentences are given below:

• Alice is a good girl. She is also very kind.
• The children went to the park. They had a nice time.

Here the pronouns she and they are of the same number, gender and person as the nouns Alice and children.

When two singular nouns connected by and refer to the same person, the pronoun should be singular in number.

• My friend and colleague has agreed to lend me his car.

Here the nouns my friend and colleague refer to the same person. Therefore we use a singular noun and a verb.

When two singular nouns connected by and refer to different persons, we use plural verbs and plural pronouns. Note that when the nouns refer to different persons, we use a determiner (e.g. the, my, this etc.) before each noun.

• My friend and my colleague have agreed to lend me their support. (NOT My friend and colleague have agreed to…)

When two singular nouns connected by and are preceded by each or every, the pronoun must be in the singular.

• Each boy and each girl was asked to participate in the program.

The pronoun referring back to two singular nouns joined by or, either…or or neither…nor should be singular in number.

• Either Alice or Mary will bring her violin.

• Neither John nor Peter did his homework.

When a singular noun and a plural noun are joined by or or nor the pronoun should be plural in number.

• Neither my brother nor my sisters were happy with my decision to quit the job.

Related posts:

1. What are Pronouns?
2. Nouns with Identical Singular and Plural Forms
3. Nouns with Different Meanings in the Singular and the Plural