I could try you could try she could try we could try you could try they could try
V-ing form
I could be trying you could be trying she could be trying we could be trying you could be trying they could be trying
Perfect
I could have tried you could have tried she could have tried we could have tried you could have tried they could have tried
V-ing perfect
I could have been trying you could have been trying she could have been trying we could have been trying you could have been trying they could have been trying
Negation
Simple form
I could not try you could not try she could not try we could not try you could not try they could not try
V-ing form
I could not be trying you could not be trying she could not be trying we could not be trying you could not be trying they could not be trying
Perfect
I could not have tried you could not have tried she could not have tried we could not have tried you could not have tried they could not have tried
V-ing perfect
I could not have been trying you could not have been trying she could not have been trying we could not have been trying you could not have been trying they could not have been trying
Interrogative form
Simple form
could I try? could you try? could she try? could we try? could you try? could they try?
V-ing form
could I be trying? could you be trying? could she be trying? could we be trying? could you be trying? could they be trying?
Perfect
could I have tried? could you have tried? could she have tried? could we have tried? could you have tried? could they have tried?
V-ing perfect
could I have been trying? could you have been trying? could she have been trying? could we have been trying? could you have been trying? could they have been trying?
Interro-negative form
Simple form
could I not try? could you not try? could she not try? could we not try? could you not try? could they not try?
V-ing form
could I not be trying? could you not be trying? could she not be trying? could we not be trying? could you not be trying? could they not be trying?
Perfect
could I not have tried? could you not have tried? could she not have tried? could we not have tried? could you not have tried? could they not have tried?
V-ing perfect
could I not have been trying? could you not have been trying? could she not have been trying? could we not have been trying? could you not have been trying? could they not have been trying?