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