I could treat you could treat he could treat we could treat you could treat they could treat
V-ing form
I could be treating you could be treating he could be treating we could be treating you could be treating they could be treating
Perfect
I could have treated you could have treated he 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 he could have been treating we could have been treating you could have been treating they could have been treating
Negation
Simple form
I could not treat you could not treat he could not treat we could not treat you could not treat they could not treat
V-ing form
I could not be treating you could not be treating he could not be treating we could not be treating you could not be treating they could not be treating
Perfect
I could not have treated you could not have treated he could not have treated we could not have treated you could not have treated they could not have treated
V-ing perfect
I could not have been treating you could not have been treating he could not have been treating we could not have been treating you could not have been treating they could not have been treating
Interrogative form
Simple form
could I treat? could you treat? could he treat? could we treat? could you treat? could they treat?
V-ing form
could I be treating? could you be treating? could he be treating? could we be treating? could you be treating? could they be treating?
Perfect
could I have treated? could you have treated? could he 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 he have been treating? could we have been treating? could you have been treating? could they have been treating?
Interro-negative form
Simple form
could I not treat? could you not treat? could he not treat? could we not treat? could you not treat? could they not treat?
V-ing form
could I not be treating? could you not be treating? could he not be treating? could we not be treating? could you not be treating? could they not be treating?
Perfect
could I not have treated? could you not have treated? could he not have treated? could we not have treated? could you not have treated? could they not have treated?
V-ing perfect
could I not have been treating? could you not have been treating? could he not have been treating? could we not have been treating? could you not have been treating? could they not have been treating?