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 couldn't reply you couldn't reply he couldn't reply we couldn't reply you couldn't reply they couldn't reply
V-ing form
I couldn't be replying you couldn't be replying he couldn't be replying we couldn't be replying you couldn't be replying they couldn't be replying
Perfect
I couldn't have replied you couldn't have replied he couldn't have replied we couldn't have replied you couldn't have replied they couldn't have replied
V-ing perfect
I couldn't have been replying you couldn't have been replying he couldn't have been replying we couldn't have been replying you couldn't have been replying they couldn't 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
couldn't I reply? couldn't you reply? couldn't he reply? couldn't we reply? couldn't you reply? couldn't they reply?
V-ing form
couldn't I be replying? couldn't you be replying? couldn't he be replying? couldn't we be replying? couldn't you be replying? couldn't they be replying?
Perfect
couldn't I have replied? couldn't you have replied? couldn't he have replied? couldn't we have replied? couldn't you have replied? couldn't they have replied?
V-ing perfect
couldn't I have been replying? couldn't you have been replying? couldn't he have been replying? couldn't we have been replying? couldn't you have been replying? couldn't they have been replying?