I could perk you could perk she could perk we could perk you could perk they could perk
V-ing form
I could be perking you could be perking she could be perking we could be perking you could be perking they could be perking
Perfect
I could have perked you could have perked she 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 she 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 she 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 she 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 she 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 she 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 she perk? could we perk? could you perk? could they perk?
V-ing form
could I be perking? could you be perking? could she be perking? could we be perking? could you be perking? could they be perking?
Perfect
could I have perked? could you have perked? could she 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 she 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 she 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 she 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 she 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 she have been perking? couldn't we have been perking? couldn't you have been perking? couldn't they have been perking?