I could tug you could tug he could tug we could tug you could tug they could tug
V-ing form
I could be tugging you could be tugging he could be tugging we could be tugging you could be tugging they could be tugging
Perfect
I could have tugged you could have tugged he could have tugged we could have tugged you could have tugged they could have tugged
V-ing perfect
I could have been tugging you could have been tugging he could have been tugging we could have been tugging you could have been tugging they could have been tugging
Negation
Simple form
I could not tug you could not tug he could not tug we could not tug you could not tug they could not tug
V-ing form
I could not be tugging you could not be tugging he could not be tugging we could not be tugging you could not be tugging they could not be tugging
Perfect
I could not have tugged you could not have tugged he could not have tugged we could not have tugged you could not have tugged they could not have tugged
V-ing perfect
I could not have been tugging you could not have been tugging he could not have been tugging we could not have been tugging you could not have been tugging they could not have been tugging
Interrogative form
Simple form
could I tug? could you tug? could he tug? could we tug? could you tug? could they tug?
V-ing form
could I be tugging? could you be tugging? could he be tugging? could we be tugging? could you be tugging? could they be tugging?
Perfect
could I have tugged? could you have tugged? could he have tugged? could we have tugged? could you have tugged? could they have tugged?
V-ing perfect
could I have been tugging? could you have been tugging? could he have been tugging? could we have been tugging? could you have been tugging? could they have been tugging?
Interro-negative form
Simple form
could I not tug? could you not tug? could he not tug? could we not tug? could you not tug? could they not tug?
V-ing form
could I not be tugging? could you not be tugging? could he not be tugging? could we not be tugging? could you not be tugging? could they not be tugging?
Perfect
could I not have tugged? could you not have tugged? could he not have tugged? could we not have tugged? could you not have tugged? could they not have tugged?
V-ing perfect
could I not have been tugging? could you not have been tugging? could he not have been tugging? could we not have been tugging? could you not have been tugging? could they not have been tugging?