在英语语法中，当句子所描述的动作或状态是经常性、习惯性的，且主语为第三人称单数时，谓语动词需要采用第三人称单数形式。
关于第三人称单数动词的变形规则，可以归纳为以下几点：
- 在大多数情况下，直接在动词原形后加上后缀 -s。
- 例如：He plays basketball every day. She walks to school in the morning.
- 对于那些以字母 s、x、z、sh、ch、o 结尾的动词，需要在动词原形后直接加上后缀 -es。
- 例如：The bus passes by every hour. The fox chases the rabbit quickly.
- 对于以字母 y 结尾的动词，如果 y 前面是辅音字母，则需要将 y 变成 i，然后再加上后缀 -es。
- 例如：The baby cries loudly. The city lies on a river.
- 对于以字母 y 结尾的动词，如果 y 前面是元音字母，则直接在动词原形后加上后缀 -s。
- 例如：The boy plays basketball with his friends. The day ends at sunset.
- 特殊动词 be 的第三人称单数形式是 is。
- 例如：The cat is on the table. The sun is shining brightly.
- 特殊动词 have 的第三人称单数形式是 has。
- 例如：He has a car. She has a lot of friends.
其他常见动词的第三人称单数形式
- 动词 go 的第三人称单数形式是 goes。
- 例如：The man goes to work every day. The woman goes to the store on weekends.
- 动词 do 的第三人称单数形式是 does。
- 例如：The child does his homework every evening. The dog does not bark at night.
- 动词 say 的第三人称单数形式是 says。
- 例如：The teacher says “Hello” to the students every morning. The bird says “Tweet” when it is happy.
综合示例
- He plays basketball. (他每天打篮球。)
- She walks to school. (她走路去上学。)
- The bus passes by. (公共汽车每小时经过一次。)
- The fox chases the rabbit. (狐狸追着兔子跑。)
- The baby cries. (婴儿在哭泣。)
- The city lies on a river. (城市坐落在河边。)
- The boy plays basketball. (男孩打篮球。)
- The day ends. (白天结束了。)
- The cat is on the table. (猫在桌子上。)
- The sun is shining. (太阳在照耀。)
- He has a car. (他有一辆车。)
- She has a lot of friends. (她有很多朋友。)
- The man goes to work. (男人去上班。)
- The woman goes to the store. (女人去商店。)
- The child does his homework. (孩子做他的家庭作业。)
- The dog does not bark. (狗不叫。)
- The teacher says “Hello” to the students. (老师向学生们说“你好”。)
- The bird says “Tweet”. (小鸟说“啁啁”。)