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