I could reply you could reply he could reply we could reply you could reply they could reply
V-ing form
I could be replying you could be replying he could be replying we could be replying you could be replying they could be replying
Perfect
I could have replied you could have replied he could have replied we could have replied you could have replied they could have replied
V-ing perfect
I could have been replying you could have been replying he could have been replying we could have been replying you could have been replying they could have been replying
Negation
Simple form
I could not reply you could not reply he could not reply we could not reply you could not reply they could not reply
V-ing form
I could not be replying you could not be replying he could not be replying we could not be replying you could not be replying they could not be replying
Perfect
I could not have replied you could not have replied he could not have replied we could not have replied you could not have replied they could not have replied
V-ing perfect
I could not have been replying you could not have been replying he could not have been replying we could not have been replying you could not have been replying they could not have been replying
Interrogative form
Simple form
could I reply? could you reply? could he reply? could we reply? could you reply? could they reply?
V-ing form
could I be replying? could you be replying? could he be replying? could we be replying? could you be replying? could they be replying?
Perfect
could I have replied? could you have replied? could he have replied? could we have replied? could you have replied? could they have replied?
V-ing perfect
could I have been replying? could you have been replying? could he have been replying? could we have been replying? could you have been replying? could they have been replying?
Interro-negative form
Simple form
could I not reply? could you not reply? could he not reply? could we not reply? could you not reply? could they not reply?
V-ing form
could I not be replying? could you not be replying? could he not be replying? could we not be replying? could you not be replying? could they not be replying?
Perfect
could I not have replied? could you not have replied? could he not have replied? could we not have replied? could you not have replied? could they not have replied?
V-ing perfect
could I not have been replying? could you not have been replying? could he not have been replying? could we not have been replying? could you not have been replying? could they not have been replying?