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