1.语法一致的原则
（1）以单数名词或代词，动词不定式短语作主语时，谓语动词要用单数;主语为复数时，谓语用复数，例如：
He goes to school early every morning.
The children are playing outside.
To work hard is necessary for a student.
（2）由and或both……and连接的并列成分作主语时，谓语动词用复数。例如：
Both he and I are right.
Mr Black and Mrs Black have a son called Tom.
但并列主语如果指的是同一人，同一事物或同一概念，谓语动词用单数。例如：
His teacher and friend is a beautiful girl.
The poet and writer has come.
（3）由and连接的并列单数主语之前如果分别由each, every修饰时，其谓语动词要用单数形式。例如：
In our country every boy and every girl has the right to receive education.
Each man and each woman is asked to help.
（4）主语是单数时，尽管后面跟有 but ,except, besides, with 等介词短语，谓语动词仍用单数。例如：
The teacher with his students is going to visit the museum.
Nobody but two boys was late for class.
Bread and butter is a daily food in the west.