The rule
- Singular subject → add -s to the verb: He runs.
- Plural subject → no -s: They run.
Common cases
- 'I' and 'you' take the plural verb: I run, you run.
- Wrong: She run. Right: She runs.
Key idea
A singular subject takes a verb with -s (he plays); a plural subject takes a verb without -s (they play).
Remember
He, she and it take the -s form of the verb.