could thicken
Regular verb: thicken - thickened- thickened

Affirmation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I could thicken
you could thicken
she could thicken
we could thicken
you could thicken
they could thicken 	I could be thickening
you could be thickening
she could be thickening
we could be thickening
you could be thickening
they could be thickening	I could have thickened
you could have thickened
she could have thickened
we could have thickened
you could have thickened
they could have thickened	I could have been thickening
you could have been thickening
she could have been thickening
we could have been thickening
you could have been thickening
they could have been thickening	

Negation 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
I couldn't thicken
you couldn't thicken
she couldn't thicken
we couldn't thicken
you couldn't thicken
they couldn't thicken 	I couldn't be thickening
you couldn't be thickening
she couldn't be thickening
we couldn't be thickening
you couldn't be thickening
they couldn't be thickening	I couldn't have thickened
you couldn't have thickened
she couldn't have thickened
we couldn't have thickened
you couldn't have thickened
they couldn't have thickened	I couldn't have been thickening
you couldn't have been thickening
she couldn't have been thickening
we couldn't have been thickening
you couldn't have been thickening
they couldn't have been thickening	

Interrogative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
could I thicken?
could you thicken?
could she thicken?
could we thicken?
could you thicken?
could they thicken? 	could I be thickening?
could you be thickening?
could she be thickening?
could we be thickening?
could you be thickening?
could they be thickening? 	could I have thickened?
could you have thickened?
could she have thickened?
could we have thickened?
could you have thickened?
could they have thickened? 	could I have been thickening?
could you have been thickening?
could she have been thickening?
could we have been thickening?
could you have been thickening?
could they have been thickening? 	

Interro-negative form 	
Simple form 	V-ing form 	Perfect 	V-ing perfect 	
couldn't I thicken?
couldn't you thicken?
couldn't she thicken?
couldn't we thicken?
couldn't you thicken?
couldn't they thicken? 	couldn't I be thickening?
couldn't you be thickening?
couldn't she be thickening?
couldn't we be thickening?
couldn't you be thickening?
couldn't they be thickening? 	couldn't I have thickened?
couldn't you have thickened?
couldn't she have thickened?
couldn't we have thickened?
couldn't you have thickened?
couldn't they have thickened? 	couldn't I have been thickening?
couldn't you have been thickening?
couldn't she have been thickening?
couldn't we have been thickening?
couldn't you have been thickening?
couldn't they have been thickening?