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 couldn't treat you couldn't treat he 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 he 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 he 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 he 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 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
couldn't I treat? couldn't you treat? couldn't he 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 he 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 he 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 he have been treating? couldn't we have been treating? couldn't you have been treating? couldn't they have been treating?