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