What is have to / has to? How it different from have/ has ?

 What is have to / has to? How it different from have/ has ? 

Have to / Has to :

They are semi-model auxiliary verbs . They show obligation, necessity and responsibility. 

Have to = use with plural subject 

Has to = use with singular subject 

For example :

1: I have to take your class . 

2: She has to learn the test. 

3: You have to complete your work . 

4: Ali has to go early. 

5: They have to work at night .

6: He has to speak English. 

7: We have to join the class. 

Have / Has : 

They are main verbs . They show possession and diseases. 

Have = use with plural subject 

Has= use with singular subject 

For example: 

1: She has a beautiful cat . 

2: I have an English book .

3: He has a headache . 

NOTE : 

1: She has a beautiful cat . [ positive sentence ] 

2: She does not have a beautiful cat .[ negative sentence ] 

=> Has is only use in positive sentences with singular subject . 

=> Have is used both positive and negative sentences . And also use with singular subject in negative sentences .