I could double-check you could double-check he could double-check we could double-check you could double-check they could double-check
V-ing form
I could be double-checking you could be double-checking he could be double-checking we could be double-checking you could be double-checking they could be double-checking
Perfect
I could have double-checked you could have double-checked he could have double-checked we could have double-checked you could have double-checked they could have double-checked
V-ing perfect
I could have been double-checking you could have been double-checking he could have been double-checking we could have been double-checking you could have been double-checking they could have been double-checking
Negation
Simple form
I could not double-check you could not double-check he could not double-check we could not double-check you could not double-check they could not double-check
V-ing form
I could not be double-checking you could not be double-checking he could not be double-checking we could not be double-checking you could not be double-checking they could not be double-checking
Perfect
I could not have double-checked you could not have double-checked he could not have double-checked we could not have double-checked you could not have double-checked they could not have double-checked
V-ing perfect
I could not have been double-checking you could not have been double-checking he could not have been double-checking we could not have been double-checking you could not have been double-checking they could not have been double-checking
Interrogative form
Simple form
could I double-check? could you double-check? could he double-check? could we double-check? could you double-check? could they double-check?
V-ing form
could I be double-checking? could you be double-checking? could he be double-checking? could we be double-checking? could you be double-checking? could they be double-checking?
Perfect
could I have double-checked? could you have double-checked? could he have double-checked? could we have double-checked? could you have double-checked? could they have double-checked?
V-ing perfect
could I have been double-checking? could you have been double-checking? could he have been double-checking? could we have been double-checking? could you have been double-checking? could they have been double-checking?
Interro-negative form
Simple form
could I not double-check? could you not double-check? could he not double-check? could we not double-check? could you not double-check? could they not double-check?
V-ing form
could I not be double-checking? could you not be double-checking? could he not be double-checking? could we not be double-checking? could you not be double-checking? could they not be double-checking?
Perfect
could I not have double-checked? could you not have double-checked? could he not have double-checked? could we not have double-checked? could you not have double-checked? could they not have double-checked?
V-ing perfect
could I not have been double-checking? could you not have been double-checking? could he not have been double-checking? could we not have been double-checking? could you not have been double-checking? could they not have been double-checking?