could perturb
Regular verb: perturb - perturbed- perturbed

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could perturb
you could perturb
he could perturb
we could perturb
you could perturb
they could perturb 	I could be perturbing
you could be perturbing
he could be perturbing
we could be perturbing
you could be perturbing
they could be perturbing	I could have perturbed
you could have perturbed
he could have perturbed
we could have perturbed
you could have perturbed
they could have perturbed	I could have been perturbing
you could have been perturbing
he could have been perturbing
we could have been perturbing
you could have been perturbing
they could have been perturbing	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't perturb
you couldn't perturb
he couldn't perturb
we couldn't perturb
you couldn't perturb
they couldn't perturb 	I couldn't be perturbing
you couldn't be perturbing
he couldn't be perturbing
we couldn't be perturbing
you couldn't be perturbing
they couldn't be perturbing	I couldn't have perturbed
you couldn't have perturbed
he couldn't have perturbed
we couldn't have perturbed
you couldn't have perturbed
they couldn't have perturbed	I couldn't have been perturbing
you couldn't have been perturbing
he couldn't have been perturbing
we couldn't have been perturbing
you couldn't have been perturbing
they couldn't have been perturbing	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I perturb?
could you perturb?
could he perturb?
could we perturb?
could you perturb?
could they perturb? 	could I be perturbing?
could you be perturbing?
could he be perturbing?
could we be perturbing?
could you be perturbing?
could they be perturbing? 	could I have perturbed?
could you have perturbed?
could he have perturbed?
could we have perturbed?
could you have perturbed?
could they have perturbed? 	could I have been perturbing?
could you have been perturbing?
could he have been perturbing?
could we have been perturbing?
could you have been perturbing?
could they have been perturbing? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I perturb?
couldn't you perturb?
couldn't he perturb?
couldn't we perturb?
couldn't you perturb?
couldn't they perturb? 	couldn't I be perturbing?
couldn't you be perturbing?
couldn't he be perturbing?
couldn't we be perturbing?
couldn't you be perturbing?
couldn't they be perturbing? 	couldn't I have perturbed?
couldn't you have perturbed?
couldn't he have perturbed?
couldn't we have perturbed?
couldn't you have perturbed?
couldn't they have perturbed? 	couldn't I have been perturbing?
couldn't you have been perturbing?
couldn't he have been perturbing?
couldn't we have been perturbing?
couldn't you have been perturbing?
couldn't they have been perturbing?