I could delve you could delve she could delve we could delve you could delve they could delve
V-ing form
I could be delving you could be delving she could be delving we could be delving you could be delving they could be delving
Perfect
I could have delved you could have delved she 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 she could have been delving we could have been delving you could have been delving they could have been delving
Negation
Simple form
I couldn't delve you couldn't delve she couldn't delve we couldn't delve you couldn't delve they couldn't delve
V-ing form
I couldn't be delving you couldn't be delving she couldn't be delving we couldn't be delving you couldn't be delving they couldn't be delving
Perfect
I couldn't have delved you couldn't have delved she couldn't have delved we couldn't have delved you couldn't have delved they couldn't have delved
V-ing perfect
I couldn't have been delving you couldn't have been delving she couldn't have been delving we couldn't have been delving you couldn't have been delving they couldn't have been delving
Interrogative form
Simple form
could I delve? could you delve? could she delve? could we delve? could you delve? could they delve?
V-ing form
could I be delving? could you be delving? could she be delving? could we be delving? could you be delving? could they be delving?
Perfect
could I have delved? could you have delved? could she 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 she have been delving? could we have been delving? could you have been delving? could they have been delving?
Interro-negative form
Simple form
couldn't I delve? couldn't you delve? couldn't she delve? couldn't we delve? couldn't you delve? couldn't they delve?
V-ing form
couldn't I be delving? couldn't you be delving? couldn't she be delving? couldn't we be delving? couldn't you be delving? couldn't they be delving?
Perfect
couldn't I have delved? couldn't you have delved? couldn't she have delved? couldn't we have delved? couldn't you have delved? couldn't they have delved?
V-ing perfect
couldn't I have been delving? couldn't you have been delving? couldn't she have been delving? couldn't we have been delving? couldn't you have been delving? couldn't they have been delving?