I could perk you could perk he could perk we could perk you could perk they could perk
V-ing form
I could be perking you could be perking he could be perking we could be perking you could be perking they could be perking
Perfect
I could have perked you could have perked he could have perked we could have perked you could have perked they could have perked
V-ing perfect
I could have been perking you could have been perking he could have been perking we could have been perking you could have been perking they could have been perking
Negation
Simple form
I couldn't perk you couldn't perk he couldn't perk we couldn't perk you couldn't perk they couldn't perk
V-ing form
I couldn't be perking you couldn't be perking he couldn't be perking we couldn't be perking you couldn't be perking they couldn't be perking
Perfect
I couldn't have perked you couldn't have perked he couldn't have perked we couldn't have perked you couldn't have perked they couldn't have perked
V-ing perfect
I couldn't have been perking you couldn't have been perking he couldn't have been perking we couldn't have been perking you couldn't have been perking they couldn't have been perking
Interrogative form
Simple form
could I perk? could you perk? could he perk? could we perk? could you perk? could they perk?
V-ing form
could I be perking? could you be perking? could he be perking? could we be perking? could you be perking? could they be perking?
Perfect
could I have perked? could you have perked? could he have perked? could we have perked? could you have perked? could they have perked?
V-ing perfect
could I have been perking? could you have been perking? could he have been perking? could we have been perking? could you have been perking? could they have been perking?
Interro-negative form
Simple form
couldn't I perk? couldn't you perk? couldn't he perk? couldn't we perk? couldn't you perk? couldn't they perk?
V-ing form
couldn't I be perking? couldn't you be perking? couldn't he be perking? couldn't we be perking? couldn't you be perking? couldn't they be perking?
Perfect
couldn't I have perked? couldn't you have perked? couldn't he have perked? couldn't we have perked? couldn't you have perked? couldn't they have perked?
V-ing perfect
couldn't I have been perking? couldn't you have been perking? couldn't he have been perking? couldn't we have been perking? couldn't you have been perking? couldn't they have been perking?