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