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