I could japan you could japan he could japan we could japan you could japan they could japan
V-ing form
I could be japaning you could be japaning he could be japaning we could be japaning you could be japaning they could be japaning
Perfect
I could have japaned you could have japaned he could have japaned we could have japaned you could have japaned they could have japaned
V-ing perfect
I could have been japaning you could have been japaning he could have been japaning we could have been japaning you could have been japaning they could have been japaning
Negation
Simple form
I could not japan you could not japan he could not japan we could not japan you could not japan they could not japan
V-ing form
I could not be japaning you could not be japaning he could not be japaning we could not be japaning you could not be japaning they could not be japaning
Perfect
I could not have japaned you could not have japaned he could not have japaned we could not have japaned you could not have japaned they could not have japaned
V-ing perfect
I could not have been japaning you could not have been japaning he could not have been japaning we could not have been japaning you could not have been japaning they could not have been japaning
Interrogative form
Simple form
could I japan? could you japan? could he japan? could we japan? could you japan? could they japan?
V-ing form
could I be japaning? could you be japaning? could he be japaning? could we be japaning? could you be japaning? could they be japaning?
Perfect
could I have japaned? could you have japaned? could he have japaned? could we have japaned? could you have japaned? could they have japaned?
V-ing perfect
could I have been japaning? could you have been japaning? could he have been japaning? could we have been japaning? could you have been japaning? could they have been japaning?
Interro-negative form
Simple form
could I not japan? could you not japan? could he not japan? could we not japan? could you not japan? could they not japan?
V-ing form
could I not be japaning? could you not be japaning? could he not be japaning? could we not be japaning? could you not be japaning? could they not be japaning?
Perfect
could I not have japaned? could you not have japaned? could he not have japaned? could we not have japaned? could you not have japaned? could they not have japaned?
V-ing perfect
could I not have been japaning? could you not have been japaning? could he not have been japaning? could we not have been japaning? could you not have been japaning? could they not have been japaning?