I could decay you could decay he could decay we could decay you could decay they could decay
V-ing form
I could be decaying you could be decaying he could be decaying we could be decaying you could be decaying they could be decaying
Perfect
I could have decayed you could have decayed he could have decayed we could have decayed you could have decayed they could have decayed
V-ing perfect
I could have been decaying you could have been decaying he could have been decaying we could have been decaying you could have been decaying they could have been decaying
Negation
Simple form
I could not decay you could not decay he could not decay we could not decay you could not decay they could not decay
V-ing form
I could not be decaying you could not be decaying he could not be decaying we could not be decaying you could not be decaying they could not be decaying
Perfect
I could not have decayed you could not have decayed he could not have decayed we could not have decayed you could not have decayed they could not have decayed
V-ing perfect
I could not have been decaying you could not have been decaying he could not have been decaying we could not have been decaying you could not have been decaying they could not have been decaying
Interrogative form
Simple form
could I decay? could you decay? could he decay? could we decay? could you decay? could they decay?
V-ing form
could I be decaying? could you be decaying? could he be decaying? could we be decaying? could you be decaying? could they be decaying?
Perfect
could I have decayed? could you have decayed? could he have decayed? could we have decayed? could you have decayed? could they have decayed?
V-ing perfect
could I have been decaying? could you have been decaying? could he have been decaying? could we have been decaying? could you have been decaying? could they have been decaying?
Interro-negative form
Simple form
could I not decay? could you not decay? could he not decay? could we not decay? could you not decay? could they not decay?
V-ing form
could I not be decaying? could you not be decaying? could he not be decaying? could we not be decaying? could you not be decaying? could they not be decaying?
Perfect
could I not have decayed? could you not have decayed? could he not have decayed? could we not have decayed? could you not have decayed? could they not have decayed?
V-ing perfect
could I not have been decaying? could you not have been decaying? could he not have been decaying? could we not have been decaying? could you not have been decaying? could they not have been decaying?