could stumble
Regular verb: stumble - stumbled- stumbled

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could stumble
you could stumble
she could stumble
we could stumble
you could stumble
they could stumble 	I could be stumbling
you could be stumbling
she could be stumbling
we could be stumbling
you could be stumbling
they could be stumbling	I could have stumbled
you could have stumbled
she could have stumbled
we could have stumbled
you could have stumbled
they could have stumbled	I could have been stumbling
you could have been stumbling
she could have been stumbling
we could have been stumbling
you could have been stumbling
they could have been stumbling	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't stumble
you couldn't stumble
she couldn't stumble
we couldn't stumble
you couldn't stumble
they couldn't stumble 	I couldn't be stumbling
you couldn't be stumbling
she couldn't be stumbling
we couldn't be stumbling
you couldn't be stumbling
they couldn't be stumbling	I couldn't have stumbled
you couldn't have stumbled
she couldn't have stumbled
we couldn't have stumbled
you couldn't have stumbled
they couldn't have stumbled	I couldn't have been stumbling
you couldn't have been stumbling
she couldn't have been stumbling
we couldn't have been stumbling
you couldn't have been stumbling
they couldn't have been stumbling	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I stumble?
could you stumble?
could she stumble?
could we stumble?
could you stumble?
could they stumble? 	could I be stumbling?
could you be stumbling?
could she be stumbling?
could we be stumbling?
could you be stumbling?
could they be stumbling? 	could I have stumbled?
could you have stumbled?
could she have stumbled?
could we have stumbled?
could you have stumbled?
could they have stumbled? 	could I have been stumbling?
could you have been stumbling?
could she have been stumbling?
could we have been stumbling?
could you have been stumbling?
could they have been stumbling? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I stumble?
couldn't you stumble?
couldn't she stumble?
couldn't we stumble?
couldn't you stumble?
couldn't they stumble? 	couldn't I be stumbling?
couldn't you be stumbling?
couldn't she be stumbling?
couldn't we be stumbling?
couldn't you be stumbling?
couldn't they be stumbling? 	couldn't I have stumbled?
couldn't you have stumbled?
couldn't she have stumbled?
couldn't we have stumbled?
couldn't you have stumbled?
couldn't they have stumbled? 	couldn't I have been stumbling?
couldn't you have been stumbling?
couldn't she have been stumbling?
couldn't we have been stumbling?
couldn't you have been stumbling?
couldn't they have been stumbling?