I could delve you could delve he could delve we could delve you could delve they could delve
V-ing form
I could be delving you could be delving he could be delving we could be delving you could be delving they could be delving
Perfect
I could have delved you could have delved he could have delved we could have delved you could have delved they could have delved
V-ing perfect
I could have been delving you could have been delving he could have been delving we could have been delving you could have been delving they could have been delving
Negation
Simple form
I could not delve you could not delve he could not delve we could not delve you could not delve they could not delve
V-ing form
I could not be delving you could not be delving he could not be delving we could not be delving you could not be delving they could not be delving
Perfect
I could not have delved you could not have delved he could not have delved we could not have delved you could not have delved they could not have delved
V-ing perfect
I could not have been delving you could not have been delving he could not have been delving we could not have been delving you could not have been delving they could not have been delving
Interrogative form
Simple form
could I delve? could you delve? could he delve? could we delve? could you delve? could they delve?
V-ing form
could I be delving? could you be delving? could he be delving? could we be delving? could you be delving? could they be delving?
Perfect
could I have delved? could you have delved? could he have delved? could we have delved? could you have delved? could they have delved?
V-ing perfect
could I have been delving? could you have been delving? could he have been delving? could we have been delving? could you have been delving? could they have been delving?
Interro-negative form
Simple form
could I not delve? could you not delve? could he not delve? could we not delve? could you not delve? could they not delve?
V-ing form
could I not be delving? could you not be delving? could he not be delving? could we not be delving? could you not be delving? could they not be delving?
Perfect
could I not have delved? could you not have delved? could he not have delved? could we not have delved? could you not have delved? could they not have delved?
V-ing perfect
could I not have been delving? could you not have been delving? could he not have been delving? could we not have been delving? could you not have been delving? could they not have been delving?