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