I could mast you could mast she could mast we could mast you could mast they could mast
V-ing form
I could be masting you could be masting she could be masting we could be masting you could be masting they could be masting
Perfect
I could have masted you could have masted she 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 she 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 she 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 she 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 she 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 she 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 she mast? could we mast? could you mast? could they mast?
V-ing form
could I be masting? could you be masting? could she be masting? could we be masting? could you be masting? could they be masting?
Perfect
could I have masted? could you have masted? could she 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 she 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 she 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 she 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 she 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 she have been masting? couldn't we have been masting? couldn't you have been masting? couldn't they have been masting?