I could fax you could fax he could fax we could fax you could fax they could fax
V-ing form
I could be faxing you could be faxing he could be faxing we could be faxing you could be faxing they could be faxing
Perfect
I could have faxed you could have faxed he could have faxed we could have faxed you could have faxed they could have faxed
V-ing perfect
I could have been faxing you could have been faxing he could have been faxing we could have been faxing you could have been faxing they could have been faxing
Negation
Simple form
I could not fax you could not fax he could not fax we could not fax you could not fax they could not fax
V-ing form
I could not be faxing you could not be faxing he could not be faxing we could not be faxing you could not be faxing they could not be faxing
Perfect
I could not have faxed you could not have faxed he could not have faxed we could not have faxed you could not have faxed they could not have faxed
V-ing perfect
I could not have been faxing you could not have been faxing he could not have been faxing we could not have been faxing you could not have been faxing they could not have been faxing
Interrogative form
Simple form
could I fax? could you fax? could he fax? could we fax? could you fax? could they fax?
V-ing form
could I be faxing? could you be faxing? could he be faxing? could we be faxing? could you be faxing? could they be faxing?
Perfect
could I have faxed? could you have faxed? could he have faxed? could we have faxed? could you have faxed? could they have faxed?
V-ing perfect
could I have been faxing? could you have been faxing? could he have been faxing? could we have been faxing? could you have been faxing? could they have been faxing?
Interro-negative form
Simple form
could I not fax? could you not fax? could he not fax? could we not fax? could you not fax? could they not fax?
V-ing form
could I not be faxing? could you not be faxing? could he not be faxing? could we not be faxing? could you not be faxing? could they not be faxing?
Perfect
could I not have faxed? could you not have faxed? could he not have faxed? could we not have faxed? could you not have faxed? could they not have faxed?
V-ing perfect
could I not have been faxing? could you not have been faxing? could he not have been faxing? could we not have been faxing? could you not have been faxing? could they not have been faxing?