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