could tremble
Regular verb: tremble - trembled- trembled

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could tremble
you could tremble
she could tremble
we could tremble
you could tremble
they could tremble 	I could be trembling
you could be trembling
she could be trembling
we could be trembling
you could be trembling
they could be trembling	I could have trembled
you could have trembled
she could have trembled
we could have trembled
you could have trembled
they could have trembled	I could have been trembling
you could have been trembling
she could have been trembling
we could have been trembling
you could have been trembling
they could have been trembling	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't tremble
you couldn't tremble
she couldn't tremble
we couldn't tremble
you couldn't tremble
they couldn't tremble 	I couldn't be trembling
you couldn't be trembling
she couldn't be trembling
we couldn't be trembling
you couldn't be trembling
they couldn't be trembling	I couldn't have trembled
you couldn't have trembled
she couldn't have trembled
we couldn't have trembled
you couldn't have trembled
they couldn't have trembled	I couldn't have been trembling
you couldn't have been trembling
she couldn't have been trembling
we couldn't have been trembling
you couldn't have been trembling
they couldn't have been trembling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I tremble?
could you tremble?
could she tremble?
could we tremble?
could you tremble?
could they tremble? 	could I be trembling?
could you be trembling?
could she be trembling?
could we be trembling?
could you be trembling?
could they be trembling? 	could I have trembled?
could you have trembled?
could she have trembled?
could we have trembled?
could you have trembled?
could they have trembled? 	could I have been trembling?
could you have been trembling?
could she have been trembling?
could we have been trembling?
could you have been trembling?
could they have been trembling? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I tremble?
couldn't you tremble?
couldn't she tremble?
couldn't we tremble?
couldn't you tremble?
couldn't they tremble? 	couldn't I be trembling?
couldn't you be trembling?
couldn't she be trembling?
couldn't we be trembling?
couldn't you be trembling?
couldn't they be trembling? 	couldn't I have trembled?
couldn't you have trembled?
couldn't she have trembled?
couldn't we have trembled?
couldn't you have trembled?
couldn't they have trembled? 	couldn't I have been trembling?
couldn't you have been trembling?
couldn't she have been trembling?
couldn't we have been trembling?
couldn't you have been trembling?
couldn't they have been trembling?