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