I could doctor you could doctor he could doctor we could doctor you could doctor they could doctor
V-ing form
I could be doctoring you could be doctoring he could be doctoring we could be doctoring you could be doctoring they could be doctoring
Perfect
I could have doctored you could have doctored he could have doctored we could have doctored you could have doctored they could have doctored
V-ing perfect
I could have been doctoring you could have been doctoring he could have been doctoring we could have been doctoring you could have been doctoring they could have been doctoring
Negation
Simple form
I couldn't doctor you couldn't doctor he couldn't doctor we couldn't doctor you couldn't doctor they couldn't doctor
V-ing form
I couldn't be doctoring you couldn't be doctoring he couldn't be doctoring we couldn't be doctoring you couldn't be doctoring they couldn't be doctoring
Perfect
I couldn't have doctored you couldn't have doctored he couldn't have doctored we couldn't have doctored you couldn't have doctored they couldn't have doctored
V-ing perfect
I couldn't have been doctoring you couldn't have been doctoring he couldn't have been doctoring we couldn't have been doctoring you couldn't have been doctoring they couldn't have been doctoring
Interrogative form
Simple form
could I doctor? could you doctor? could he doctor? could we doctor? could you doctor? could they doctor?
V-ing form
could I be doctoring? could you be doctoring? could he be doctoring? could we be doctoring? could you be doctoring? could they be doctoring?
Perfect
could I have doctored? could you have doctored? could he have doctored? could we have doctored? could you have doctored? could they have doctored?
V-ing perfect
could I have been doctoring? could you have been doctoring? could he have been doctoring? could we have been doctoring? could you have been doctoring? could they have been doctoring?
Interro-negative form
Simple form
couldn't I doctor? couldn't you doctor? couldn't he doctor? couldn't we doctor? couldn't you doctor? couldn't they doctor?
V-ing form
couldn't I be doctoring? couldn't you be doctoring? couldn't he be doctoring? couldn't we be doctoring? couldn't you be doctoring? couldn't they be doctoring?
Perfect
couldn't I have doctored? couldn't you have doctored? couldn't he have doctored? couldn't we have doctored? couldn't you have doctored? couldn't they have doctored?
V-ing perfect
couldn't I have been doctoring? couldn't you have been doctoring? couldn't he have been doctoring? couldn't we have been doctoring? couldn't you have been doctoring? couldn't they have been doctoring?