I could appear you could appear she could appear we could appear you could appear they could appear
V-ing form
I could be appearing you could be appearing she could be appearing we could be appearing you could be appearing they could be appearing
Perfect
I could have appeared you could have appeared she could have appeared we could have appeared you could have appeared they could have appeared
V-ing perfect
I could have been appearing you could have been appearing she could have been appearing we could have been appearing you could have been appearing they could have been appearing
Negation
Simple form
I couldn't appear you couldn't appear she couldn't appear we couldn't appear you couldn't appear they couldn't appear
V-ing form
I couldn't be appearing you couldn't be appearing she couldn't be appearing we couldn't be appearing you couldn't be appearing they couldn't be appearing
Perfect
I couldn't have appeared you couldn't have appeared she couldn't have appeared we couldn't have appeared you couldn't have appeared they couldn't have appeared
V-ing perfect
I couldn't have been appearing you couldn't have been appearing she couldn't have been appearing we couldn't have been appearing you couldn't have been appearing they couldn't have been appearing
Interrogative form
Simple form
could I appear? could you appear? could she appear? could we appear? could you appear? could they appear?
V-ing form
could I be appearing? could you be appearing? could she be appearing? could we be appearing? could you be appearing? could they be appearing?
Perfect
could I have appeared? could you have appeared? could she have appeared? could we have appeared? could you have appeared? could they have appeared?
V-ing perfect
could I have been appearing? could you have been appearing? could she have been appearing? could we have been appearing? could you have been appearing? could they have been appearing?
Interro-negative form
Simple form
couldn't I appear? couldn't you appear? couldn't she appear? couldn't we appear? couldn't you appear? couldn't they appear?
V-ing form
couldn't I be appearing? couldn't you be appearing? couldn't she be appearing? couldn't we be appearing? couldn't you be appearing? couldn't they be appearing?
Perfect
couldn't I have appeared? couldn't you have appeared? couldn't she have appeared? couldn't we have appeared? couldn't you have appeared? couldn't they have appeared?
V-ing perfect
couldn't I have been appearing? couldn't you have been appearing? couldn't she have been appearing? couldn't we have been appearing? couldn't you have been appearing? couldn't they have been appearing?