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 couldn't double-check you couldn't double-check he couldn't double-check we couldn't double-check you couldn't double-check they couldn't double-check
V-ing form
I couldn't be double-checking you couldn't be double-checking he couldn't be double-checking we couldn't be double-checking you couldn't be double-checking they couldn't be double-checking
Perfect
I couldn't have double-checked you couldn't have double-checked he couldn't have double-checked we couldn't have double-checked you couldn't have double-checked they couldn't have double-checked
V-ing perfect
I couldn't have been double-checking you couldn't have been double-checking he couldn't have been double-checking we couldn't have been double-checking you couldn't have been double-checking they couldn't 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
couldn't I double-check? couldn't you double-check? couldn't he double-check? couldn't we double-check? couldn't you double-check? couldn't they double-check?
V-ing form
couldn't I be double-checking? couldn't you be double-checking? couldn't he be double-checking? couldn't we be double-checking? couldn't you be double-checking? couldn't they be double-checking?
Perfect
couldn't I have double-checked? couldn't you have double-checked? couldn't he have double-checked? couldn't we have double-checked? couldn't you have double-checked? couldn't they have double-checked?
V-ing perfect
couldn't I have been double-checking? couldn't you have been double-checking? couldn't he have been double-checking? couldn't we have been double-checking? couldn't you have been double-checking? couldn't they have been double-checking?