English grammar requires «has» with third person singular subjects, because the verb needs to agree with the subject in number. 5 If the subject is singular, the verb must also be singular. 5

Third person singular subjects are pronouns like «he», «she», or «it» that describe one single person or thing. 14 These subjects are followed by verbs with an «s» or «es» added to the end. 14

In the case of «has», if it is preceded by an auxiliary verb («does»), it loses its conjugation, but when there is no auxiliary, it is conjugated for third person singular. 3

Example: «She plays the piano» — «She has played the piano». 15