I could congratulate you could congratulate she could congratulate we could congratulate you could congratulate they could congratulate
V-ing form
I could be congratulating you could be congratulating she could be congratulating we could be congratulating you could be congratulating they could be congratulating
Perfect
I could have congratulated you could have congratulated she could have congratulated we could have congratulated you could have congratulated they could have congratulated
V-ing perfect
I could have been congratulating you could have been congratulating she could have been congratulating we could have been congratulating you could have been congratulating they could have been congratulating
Negation
Simple form
I could not congratulate you could not congratulate she could not congratulate we could not congratulate you could not congratulate they could not congratulate
V-ing form
I could not be congratulating you could not be congratulating she could not be congratulating we could not be congratulating you could not be congratulating they could not be congratulating
Perfect
I could not have congratulated you could not have congratulated she could not have congratulated we could not have congratulated you could not have congratulated they could not have congratulated
V-ing perfect
I could not have been congratulating you could not have been congratulating she could not have been congratulating we could not have been congratulating you could not have been congratulating they could not have been congratulating
Interrogative form
Simple form
could I congratulate? could you congratulate? could she congratulate? could we congratulate? could you congratulate? could they congratulate?
V-ing form
could I be congratulating? could you be congratulating? could she be congratulating? could we be congratulating? could you be congratulating? could they be congratulating?
Perfect
could I have congratulated? could you have congratulated? could she have congratulated? could we have congratulated? could you have congratulated? could they have congratulated?
V-ing perfect
could I have been congratulating? could you have been congratulating? could she have been congratulating? could we have been congratulating? could you have been congratulating? could they have been congratulating?
Interro-negative form
Simple form
could I not congratulate? could you not congratulate? could she not congratulate? could we not congratulate? could you not congratulate? could they not congratulate?
V-ing form
could I not be congratulating? could you not be congratulating? could she not be congratulating? could we not be congratulating? could you not be congratulating? could they not be congratulating?
Perfect
could I not have congratulated? could you not have congratulated? could she not have congratulated? could we not have congratulated? could you not have congratulated? could they not have congratulated?
V-ing perfect
could I not have been congratulating? could you not have been congratulating? could she not have been congratulating? could we not have been congratulating? could you not have been congratulating? could they not have been congratulating?