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