Subject-verb agreement is the golden rule of grammar: your subject and your verb must match in number. If the subject is singular, the verb is singular. If the subject is plural, the verb is plural.
Think of it as a dance—if one partner steps left, the other has to follow to stay in sync.
1. The Basic Rule
In the present tense, singular verbs (for he, she, it) usually end in -s, while plural verbs do not.

Subject Type	Example
Singular	The dog barks at the mailman.
Plural	The dogs bark at the mailman.

2. Tricky Scenarios
The "basics" are easy, but English loves to throw curveballs. Here are the most common traps:
Compound Subjects (The "And" Rule)
When two subjects are joined by and, they almost always take a plural verb.
Example: The cat and the dog (they) are fighting.
The "Or / Nor" Rule
When subjects are joined by or or nor, the verb agrees with the part of the subject closest to it.
Example: Neither the plate nor the cups belong in that cabinet.
Example: Neither the cups nor the plate belongs in that cabinet.
Phrases In Between
Don't let "interrupters" fool you. Ignore phrases starting with as well as, in addition to, or along with. Look only at the main subject.
Wrong: The politician, along with his aides, are expected shortly.
Right: The politician, along with his aides, is expected shortly. (The subject is just the politician).
Indefinite Pronouns
Some words sound plural but are grammatically singular: everyone, someone, nobody, each, either, neither.
Example: Everyone is happy today. (Not "Everyone are").
3. Collective Nouns
Words like group, team, committee, or family represent multiple people, but they usually act as a single unit.
Example: The team wins every game.
Note: Use a plural verb only if the members are acting individually. (The crew are disagreeing among themselves.)
4. There and Here
When a sentence starts with There or Here, the subject actually comes after the verb.
Example: There is a fly in my soup.
Example: There are three flies in my soup.